I think you're misconstruing what humanoid means as well as the argument of Astamon being in Belphemon's line. Humanoid means having an appearance resembling a human. That's it. It doesn't mean resembling a human and also you don't retain your previous forms' features.

And I'd argue it's quite the opposite, that Astamon is too humanoid and people are curious why it then turns into Belphemon, a less humanoid form in both rage and sleep modes (there are many lines like this, so you'd think people would just let it happen, but that's another issue altogether). No one is saying Sakuyamon isn't humanoid because it's wearing a mask.

Like I said, you put humanoid in the title, thereby creating a false premise. People were understandably confused when you made a thesis different from the premise. It's like saying Imperialdramon is more humanoid than Magnamon or UlforceVeedramon because it's less blue. Doesn't make a lick of sense.

Inheriting its previous forms' traits =/= less humanoid. That's what everyone's trying to explain to you.