It's hard to know where exactly to place the blame. The One Piece influence certainly doesn't help matters. Their designs creeping into Dragon Ball only serve to age down the characters.
It feels a little bit like the series is losing its identity with these discrepancies. As much as I hark on about Yamamuro's unimaginative work and would love for animators to be able throw their own touch on things, it seems the negatives that come with this are severely outweighing the positives in Super's case. For every one Iseki-esque episode, there are a hundred poor Yamamuro imitations.