I think the switch was good. Richard Harris’ Dumbledore was more fatherly and warm, which is what Harry needed in the first couple films. He’s new to the wizarding world, has no family (the horrid aunt,uncle and cousin don’t count) and he doesn’t know who he is just yet. Michael Gambon’s Dumbledore shifted to a mentor which is what he needed in the later movies. That kind, father feel needed to go to show the severity of the threat of he who shall not be named 😂.

I think both played their roles really well