Let's for a moment assume this interpretation is true, If that happens to be the case, that permanent power up should at least grant him power above 2 pieces anyway to make sense on why he wouldn't just get two pieces out of the triforce like yuganon, if your assumption is that you cannot being constantly powered from it to the full extent as the omnipotent wish. But this would make Yuga absorbing a Ganon scaling above two pieces, and then get the two pieces...?
Because the idea that Triforce pieces just set you to a certain power cap and whatever your power was prior is irrelevant is... not a thing. As I mentioned, Yuganon swells with power after obtaining the Triforce of Wisdom despite the Triforce of Wisdom consistently being portrayed as overwhelmingly inferior to the Triforce of Power. TP Zelda, who has the Triforce of Wisdom, is aware of having it and knows that it grants her mystical abilities, is completely helpless against Zant, who was granted a mere fraction of the ToP's power. Triforce pieces are at minimum additive. Yuga Ganon with the ToW and ToP >> Yuga Ganon with the ToP >> Beast Ganon >> Ganondorf with the ToP
But I think you want to imply instead that beast Ganon should just scale at the level above top Ganondorf, but I repeat would this make sense for Ganon to not get two pieces out of the triforce to power up himself further more? (still referring to alttp)
Under this same logic, why doesn't WW Ganondorf take the Triforce pieces back after Daphnes' wish in Wind Waker and effortlessly kill Link and Zelda? If you're to assume he can use the full Triforce whenever he wants, why doesn't ALTTP Ganon just wish himself into the Light World instead of devising an entire, centuries long plan to escape the Dark World? He can't use the Triforce, since he has already made his wish. Ganon using the Triforce actively is never once implied in ALTTP; every mention of him using the Triforce, or gaining power from it is in the past tense. What is portrayed as current is that he
has the Triforce, which Ganon is hoarding so nobody else can have it. Again, that's what he says at the end of the game.
I can see some residual power in him still granting the form, but I would still stay that it should be below the ToP OOT Ganon, who should still be below ALTTP Ganon, because I do believe he was powered by the artifact and in my closed thread there is also a strong simplification of that, the other room thing to me is just some kind of princess peach other room dynamic being showed as a reward for the fight
ToP Ganondorf transforms into his beast form as a result of drawing out all of the ToP's power, and cannot maintain it after being sealed. Ganon transforms into his beast form as a result of gaining the entire Triforce, and maintains it permanently, with it becoming his true form. Historia directly calls it his 'true power'. I think there's more than enough reason for Base Beast Ganon to be placed above ToP Ganon. I don't think ALTTP Ganon is using the Triforce, because as I mentioned he needs Agahnim to access the Light World and both the game, manual, and Historia (retroactively connecting it to OoT) mention the moment of him gaining immense power as being when he obtains the full Triforce initially.
Ganon in the oracles games gets beaten by a version of Link wielding a powered up noble sword, with the the Encyclopedia states has power comparable to the base Master Sword, and his resurrection being botched doesn't mean much since everything that makes reference to it only treats it as messing with his intelligence while his strength remains intact.
The fact that this is a direct sequel to a game where Ganon is defeated by a thrice upgraded Master Sword and the extremely potent Silver Arrows alone would suggest that the Oracle fight, and by extension the botched resurrection features a significantly weaker version of him. There is no reason Ganon should be beatable without the Silver Arrows (or a comparable item like the Bow of Light, which is stated to use the Triforce's power) when two games both before or after OoX have it as a requirement to take him down. You'd be suggesting that for whatever reason Lv. 3 Noble Sword >>> Lv. 3 Master Sword + Silver Arrows, despite you already mentioning that the Lv 3. Noble Sword is only ever stated as equal to the normal Master Sword.
Echoes are treated as being the same strength wise as the original, and the Echo Ganon is treated as about as much of a threat as the echo of Volvagia or that random Gohma is.
Link is already established as a hero when he faces Ganon at the beginning, with maxed hearts and wielding both the Lv 2. Might Sword, Might Bow, and Might Bombs, which as established are amped to gain a special advantage against Null and his creatures. Even then, Ganon seems to already plan to lose so that he can pull Link through a rift. He isn't faced again until considerably later in the game. And sure, Echoes are generally 'as strong' as a baseline, but if they are strictly on the same level of the echoed beings with no variation, how come Volvagia is 'treated as about as much of a threat' as Gohma when no appearance of Gohma has ever been equal to Volvagia in strength? Why does Null, who now has the Triforce of Power, summon Echoes of the previous bosses against Zelda when they should both now be massively superior to them with their Triforce pieces? Null can likely amp his Echoes, hence why he bothers summoning them at all at a time when both he and his enemies have grown significantly in strength.
I wouldn't put too much stock in him becoming the demon king in the downfall timeline either (Side note even though it's not 100% relevant to the point I'm making, Ganondorf is the demon king regardless if he's in his beast form or not) since if we use him permanently discarding his Gerudo form to remain in his beast form for the rest of the timeline as evidence he's still ToP level regardless if he has it or not, we'd actually need to treat him as being on the level of the complete Triforce since he was channeling and containing it's full power within himself at the moment those statements are referring to.
Yes, "Demon King" is a title used for Ganon/dorf multiple times, but in Historia's context, they are using it to refer to him transforming into Beast Ganon. I don't think anyone would disagree that he becomes the ALTTP beast as a result of his victory in Ocarina of Time. ALBW also directly states it in a way I don't think can be brushed off.
The Demon King Ganon was once just a thief—until the man broke into the Sacred Realm. There he stole the Triforce and transformed himself. — A Link Between Worlds, Painting III
But a thief of notorious repute broke into the Sacred Realm and claimed the Triforce. With its power, he became the Demon King Ganon, who sought to dominate all Hyrule. — A Link Between Worlds, Prologue
And no, I don't think you would have to scale him to the complete Triforce. OoT Ganon's transformation is a result of drawing out all of the ToP's power when he is near death, while ALTTP Ganon takes on the form without exhausting all of the Triforce's power. When we have seen numerous instances of the Triforce pieces individually having varying power, and taking into account that there are numerous statements both from when ALTTP came out, when ALBW came out, and when Historia pulled the Downfall Retcon that ALTTP Ganon gained his beast form and abilities the first time he gained the complete Triforce, we don't need to assume that means Beast Ganon is equal to the full Triforce at a baseline. We even see varying beast forms between TP and OoT, where one of them is a temporary state that Ganondorf abandons and continues to fight after using, and the other is a last ditch effort using the entire Triforce. You don't need to scale him to the full Triforce, but putting him at Volvagia tier is just not correct with what the story tells us. You'd be suggesting Yuga (who is already superior to ToW Zelda and faces Link with the Master Sword), who is both apparently around Beast Ganon tier in base form and allegedly far superior with the Triforce of Power, decides to fuse with Ganon for seemingly no reason. This is despite the fact that in the two other instances of him taking someone's Triforce piece, he treats them as insignificant and casts them aside. That's not even getting into how Yuga fusing with the Demon King is portrayed as a massive threat, mentioned independently of his Triforce piece.
I just can't get behind the idea that Ganon entered a permanent state the moment he used the Triforce, but also this permanent state apparently just amped him up by a small margin to make him equal to... Volvagia. The text is at odds with it, his showings are at odds with it, his actions and behaviors are at odds with it and the only thing the idea has going for it is a game where there is an explicit, overt reason given for why he would not be the same as he was prior.