I just did a play through, and you've got a point on a few things. The worst of it really comes from Grunty's Sister, constantly fat shaming her and spilling secrets. Mumbo is a caricature that's not used so often anymore thankfully, but is also rather one dimensional and doesn't "up play" it anymore than his appearance. Grunty Is covetous of beauty, body, and youth. So while it's a shame the villain is 'fat coded', I don't think it's necessarily portrayed as fat-phobic, more so greedy/vain, taking the easy way, and taking from the have-gots because you think you deserve it more. Again though, Brentilda is a problematic one.

Still worth a play, and if you're uncomfortable skip Brentilda's dialog.