Hello, I would like to participate in this discussion, hope we would have a good debate.
Although admittedly, I have a different opinion on Muscular's Attack Potency, specifically whether he actually strike as hard as OFA 100%, cause from my own observation, it feels like his muscle augmentation simply acts as a damage sponge rather than generating the same force to counter Deku's 100% smash, but that's just my own caveats. I would still follow the AP that Muscular has been appointed in his profile.
Attack Potency and Durability
As the Original Poster state, Muscular has around 3x Attack potency compare to Tanktop, making him having the advantage, though probably not at all times. I will explain that later.
Their durability is as equal as their Attack Potency, meaning Muscular had the advantage. But it does bear in mind that he seems to require more layers to actually defend against such
impact, meaning that both his strength and durability can change depending on his form. Such is a case when he tried to defend against Shindo's attack.
Speed and Mobility
Mobility-wise, I would say that Tanktop Master would have more flexibility compare to Muscular, seeing as the latter had to effective increase his bulk that may cause problems with being agile even if it does increase his speed. Speed-wise though, I am not sure. Speed equalized would mean that both have similar combat speed at base form, but Muscular can increase it, shown by his battle against Midoriya, seeing as when his speed and strength increase so does his
muscle mass.
How would the speed equalization affect someone like Muscular, whose base would technically be when he is not using his quirk, or maybe when we can still see his
shirt? I would like all of your opinion on that.
Abilities and Power
While I would believe that Tanktop's tanktops do increase his physical might due to the nature of the setting. There doesn't seem to be any additional unique ability that the fabric actually gave him, rather than simple physical enhancement and physique.
Muscular's Quirk though is that he produces muscle fibers that extrude from his body to form an extra layer of offense and defense, while similar, act as an external defense as damaging the muscles would not reach his original body, and he can simply reform it. From the recent chapters, we discover that the muscle fibers that he formed can wear and tear with
sufficient force and cause
uneven wrap, causing his defense and offense to weaken. It acts more of an "HP bar" rather than a "defense point". That would imply that relatively weak yet flurry strikes could weaken the bonds between the fibers to target his more vulnerable parts. Plus, he seems to require more layers of muscle fibers to tank Midoriya's
100% smash, meaning that his defense
aren't always the same and fluctuates depended on his form.
Intelligence and Skills
I would suggest that Tanktop has an advantage in this department, while as simple as his style is, he does show to practice martial arts and is a dedicated bodybuilder while Muscular is rather simple and doesn't imply any form of finesse in his strikes. Also, the manga tries to show Tanktop's skill in his throwing capabilities, implying that it is optional as a ranged attack and even as a form of
transportation? With the location that is set in, I could see Tanktop use it to get a distance if he so chooses to fight in close range.
Location
While it is Tanktop Master's homeworld, Z-city is still an abandoned city and I don't think that Tanktop has that much of a homeworld advantage it is not his hometown and both he and Muscular do live in an urban city. That said, I would say that Tanktop actually has some advantage not because it is his homeworld, but because of the debris that lay in the ghost town, and we have seen that he is willing to use the environment to his advantage.
Conclusion
Tanktop Master does have some option to actually win this in my opinion. We have already seen that Deku could actually slip into the fibers, with Tanktop's strength, I could see him tear a small section if he manages to do the same. And with the location, Tanktop may be able to use the debris as projectiles to weaken the muscle fibers, especially if he managed to throw something that has an edge or can focus the force, using his odd travel to avoid confrontation. though I do not know if he is open-minded enough to thought such a strategy.
Unfortunately, due to the uncertainty of how the speed equalization would affect Muscular. I would vote inconclusive. I would change it if someone gives some insight on the matter.