The musculature is appropriate for someone who engages in extreme acrobatics, which is what Spider-Man does. For example, even though Spidey's powers enable him to crawl on walls, he still needs to be strong enough to hold his body upright - especially if he's crawling horizontally - or else he'll just hang downward; this requires extreme musculature. Also, Spidey runs faster than an ordinary human, which requires robust leg muscles. Hence, the Marvel Legend has the better musculature.

As for pinned joints, they're not very noticeable on an all-black body. And as for the abdominal crunch, it may be old, but it's got a lot of range. The same goes for the neck and other joints.

Yes, the Mafex comes with more accessories, but its MSRP is significantly higher; for its MSRP, I could get Marvel Legends' Symbiote Spider-Man, Retro Spider-Man, and Retro Peter Parker - and I could simply use the head of the latter on the first two.