it looks too goofy even for minecraft to not use a walk/run animation while attacking and moving at once.
this can be done by adding animation(s) that override the animation of both leg groups of the player.
I know this can be done since vanilla lets the player and other entities use multiple animations at once

This request is far from trivial to implement, because all animations contain a certain amount of body rotation, which would be even goofier if not counteracted by legs.

What might be worth considering tho, is to additionally apply vanilla leg movement.

This request is far from trivial to implement, because all animations contain a certain amount of body rotation, which would be even goofier if not counteracted by legs.

What might be worth considering tho, is to additionally apply vanilla leg movement.

honestly i think applying vanilla leg movement is the best, would love to see a feature like this implemented in the future :)

I have investigated this issue.
Applying vanilla leg movement is not possible nor in an additive way, nor in a way to override.

I am unable to improve this further. Anyone is free to send pull request with improvements.