Something is amiss, as Spanky said yesterday. The velo drop is a concern and he's obviously labouring out there. Something's not right and he needs to go to the minors to try and sort it out under less pressure.
The key part of the above is "correctly".
Your post is contradictory. The 1st sentence says "myth" and the 2nd says if done incorrectly additional muscle mass will have a negative effect.
No. I posted in March 2022 that Orelvis had noticeably filled out. Whether the additional mass (quite bulked up in the upper body) was natural or intentional through workout, it seems to coincide with the onset of increased contact struggles.
Orelvis was really bulking up. I wouldn't be surprised if his bat to ball skills have been reduced even more as a result. Getting bigger isn't always better.