Going through Starmon X's scaling, it is comparable to this yield:
Seadramon storm = 4.59202024e20 joules, High 6-C.
Starmie is comparable to....
2.6003377e+21 Joules=621.4956262 gigatons
(Now since I'm stupid & can't into scientific notation.)So that's....
459,202,024,000,000,000,000 (or 459 quintillion 202 quadrillion 24 trillion) joules
Vs
2,600,337,700,000,000,000,000 (or 2 sextillion 600 quintillion 337 quadrillion 700 trillion) joules.
2,600,337,700,000,000,000,000 / 459,202,024,000,000,000,000 = 5.6627313559053476645825933903114
I have no idea how much stronger or weaker Starmie & Starmon X are compared to the things in their respective scaling chains, but for the numbers they're comparable to, the Pokemon feat is about 5.66 times higher than the Digimon feat, if my numbers are correct.
'course, Starmon X being the same as Starmon but possibly stronger may skew things.... Or is it staying at the same level of High 6-C Starmon is & ignoring the "possibly 4-C" as per the "Only High 6-C Starmon" is used?
Anyway, without accounting for Egg Moves -since Starmie's profile doesn't mention them, & IIRC, I'm unsure if we use them- let's look at their techniques.
The biggest problems for Starmie is that Starmon will probably try to put it to sleep. What can it do against this?
A. Natural Cure could cure Sleep. But this requires being out of battle for some time. Unlikely to happen unless Starmie buys time by shrinking with Minimize, hiding with Camouflage, gets Starmon confused with Confuse Ray, or manages to hide in some of Cerulean City's water.
B. Starmie's
Ultra Moo Pokedex entry says: "It rotates its geometrically shaped body to swim through the water. It always seems to be sending out mysterious radio waves."
Vs
"Saiminjutsu: Puts the enemy to sleep using strange radio waves."
Ergo, avoid sleep via "dude, radio wave interference, lol". ....Maybe? Are they even the same kind of radio waves.
C. As noted on Starmie's profile, being near it causes headaches, which may be problematic for the stamina, focus &/or aim of a close combat fighter like Starmon X, or if Starmon X wants to hypnotize; I imagine landing your melee strikes or doing proper hypnosis is harder with a persistent headache.
Another worrysome thing....
- Darkness Gear/Cog Crusher: Shoots black cogs from its face that can control Digimon they're embedded in.
Dunno if it can control non-Digimon, but if this can control Starmie, that's bad for Starmie. Duh.
Meteor Squall & Meteor Champion may also be problematic, but Starmie may be harder to hit if it's under cover of water, shrunken or camouflaged.
Illuminate's light could also help make Starmie hard to aim at.
Weaknesses & resistances applicable here is hard to figure out, because.... Well, for one, I don't know what Starmon X's electricity manipulation is. Also, Camouflage & Reflect Type.
Honestly, I have a hard time saying. Even knowing the numbers, I don't know much stronger than Starmon Starmon X is supposed to be here. If it puts Starmie to sleep, Starmie will have a rough time, but shrinking, bright light, cover of the local water, camouflage & headaches all make actually hitting Starmie tough, physically, non-physically, or with hypnosis or otherwise.
But Starmie has bad options, too, here. Tackle, Rapid Spin, Water Gun, Psywave, & maybe Bubblebeam are all pretty bad options; The last thing it wants to do is make itself an easier target for a close combat fighter & hypnosis user, even if the headaches are stronger up close.
In theory, if Starmie manages too avoid sleep enough, it could win a battle of attrition with its Regenerationn, Recover, durability amping via Harden & Cosmic Power, & the more temporary Light Screen. Swift is also unavoidable.
Confuse Ray is also nice utility, as is the telekinesis it has, which may allow it to redirect Starmon X's bubbles & meteors.
Even if there are several ways it could be avoided, it's not like Starmie knows in advance Starmon X will try to put it to sleep. It might figure it out after the first one or two times, given its supposedly high intelligence, but how much of a stamina drain will it have lost after falling asleep once or twice?
How much stamina sleeping will cost it is even harder to answer without being sure who's stronger here.
Their stamina is "High" vs "Likely very high" & their intellgence is "High, likely even for Pokemon standards" vs "The Starmon line is made up of highly skilled fighters who prefer to face the opponent head on and utilize either their mind based powers or their powers to summon meteors to overwhelm or defeat them."
So stamina is unclear, & one is PROBABLY pretty smart, & the other has simplistic tactics its biased to, that are probably predictable & exploitable -such as via hiding, range, healing & durability amping- in the long run.
Anyone else wanna chime in with some input? In any case, I have to go out now. Hope this helps!