Muscle ups are a skill and skills aren’t conducive to raw strength or hypertrophy by their very nature (because there’s a huge technical element) To actually build muscle you need either high reps on the basics or solid reps on moves that require greater strength (wall handstand push-ups etc) Same thing with legs, don’t bother with bs moves like dragon pistol squat… do all your single leg squats assisted so balance isn’t the main issue but rather hit higher volumes on your pistol and shrimp squats, and progress hamstrings to harder variations like Nordics And of course eat clean and in surplus
Using resistance bands, you can overcome that weak transition point and do many reps. You can get sufficient time under tension to build muscle. It may not be the best way to do so, but it's a fun skill to practice and improve.
Time under tension is completely overrated for muscle building. You can do an isometric hold and get as much time under tension as you like. It still won't be the most efficient way to build muscles.
The problem is that somewhere along the line, people started Calisthenics to build muscle in order not to join gyms, bu Calisthenics wasn't born for muscle gain, or rather, it was a side effect. Calisthenics was born to gain strenght and learn skills. People made a big effort to say that it was great in muscle building, and it certainly is, but it was not, and should not be the MAIN focus of those who practice Calisthenics. And I know because I've been into it for 12 years, from the day it became popular back then. How did it? Throught (mostly) hannibal for king and later Chris Heria, both of them had great physiques but the highlight of the videos were SKILLS. The body was a secondary thing. So yeah while Muscle ups might not be the best exercise for muscle building, it is a great exercise for raw pulling strenght and it should be used like such... but we can say the same about handstand pushups, front levers, planches and such... simply, if you train calisthenics for good looks ONLY then you're missing out big time (Talking generally, not to you specifically)
