The thing about Davros is that RTD had a perfect in show, already established event that could have explained away any future him looking different. The very last time we saw him in the timeline he was stealing the Doctor’s regeneration energy. That right there is all the justification needed for why he looks so vastly different. It wouldn’t explain away something like this which happens in the past, but if Gatwa ever goes up against Davros, The Witch’s Familiar is a perfect in canon reason for the change.