@ Dark
Actually, I'd say it's completely reasonable that Mega Man is comparable to Duo. In their first encounter, Duo would
kill Mega Man if the player fails to beat him in their fight as opposed to just stopping completely as soon as Mega Man's health reached a low point. Meanwhile in the previous game (Mega Man 7) when Mega Man and Bass fight for the first time, Bass would stop attacking and a small dialogue would ensue between the two to end the fight so Mega Man wouldn't be killed if the player failed to defeat him. However, this isn't the case in Mega Man 8 as Duo would kill Mega Man without hesitation, meaning he is fighting seriously at least to a degree. Duo even goes into his meteor form to combat Mega Man (the form he took to fight the Evil Energy robot). Furthermore, in other games like Mega Man 2: The Power Fighters where Duo is playable, earlier Robot Masters were able to damage Duo as well (despite losing to him of course), but it just goes to show that Mega Man (who's superior to said Robot Masters) being on par with Duo isn't far-fetched.
As for the giant robot that was able to restrain Mega Man once he got to Wily Tower, I will say it was likely done for the sake of plot since Duo wasn't formally introduced in Mega Man 8's story. Mega Man being captured and put in a helpless position was a perfect opportunity for Duo to step in and assert himself in the story (since Duo was in a mysterious light due to trashing Light's lab and attacking Mega Man moments ago at the time, but displaying signs of being good). This new and mysterious robot turns out to be one of the "good guys" in the story now as he saved Mega Man from peril as opposed to being depicted as an anatagonist. Besides, the robot caught Mega Man off guard when he restrained him and even after Duo sliced off the robot's arm,
Mega Man easily escaped it's grasp and immediately ran over to see if Rush was okay without any signs of fatigue or damage from the robot's electric attack. Sunstar wasn't fully powered in his battle with Mega Man? I don't know if you're referring to the Gigamix manga (since I haven't gotten to that part yet in the story), but in the games there's no indication that Sunstar isn't at full power, but quite the opposite as he one-shots Dr. Wily (in his Wily Capsule of course), casually destroys floors of the Wily Star in battle and shakes the entire Wily Star with his death throes (Low 5-B feat) which scales to Mega Man as he fought him toe-to-toe. Keep in mind, Sunstar didn't have any weaknesses so Mega Man fought him with his own power alone.
I beg to differ about Wily Machine 8 not being all that powerful. The cannon on the Wily Machine damaged Duo yes, but that doesn't mean that it was just more powerful than the rest of the machine. The entire Wily Machine was enhanced with Evil Energy meaning that any of it's attacks (including the cannon) were capable of damaging Duo and Mega Man tanking it's attack are justified (He even fought Bass who harnessed Evil Energy as well). This is evidenced by
Wily firing a shot of Evil Energy at Mega Man at the very beginning of their battle with him breaking free of it's grasp moments later . Additionally, when the Wily Capsule (which was in the Wily Machine before it was destroyed) is taken down by Mega Man,
Evil Energy rises from the wreckage and attacks him , suggesting that the entire machine was infected with Evil Energy the whole time. This means Mega Man was tanking attacks from the Wily Machine 8 as well as surviving assaults from Evil Energy, proving that Mega Man does scale to the likes of both Duo and Evil Energy's collision.
I just wanted to address those points and feel that Mega Man should scale to Duo and Sunstar. Actually I feel the more powerful characters in the Classic series Mega Man, Proto Man, Bass, Duo, Sunstar, King, Ra Moon and maybe even the Stardroids should scale to 5-A. Also, the calc about Wily's Satellite lasers in the Megamix manga is on Mega Man's profile if you want to explore it further. Despite there being 13 satellites initially, just one of them was enough needed to threaten the planet to follow Wily's demands since he was still bent on launching at least one in the air despite the others being destroyed.
Other than that, I completely agree with your other points.