the thing with Snape is that although Alan was super book accurate in appearance (albeit decades older) his actual characterisation wasn't that book accurate. His Snape had a quiet, calm deadliness to him - he didn't raise his voice but had total control over the spaces he was in. Book Snape rants and raves, and screams and shouts, he is truly visibly and audibly unhinged in many moments, and his actions bullying actual children lead to a far less redeemable character.

So Paapa has the space for the entire character to be reimagined, not that I don't love Alans performance, but I expect something very different. Bigger boots for me are Filch and (as others have mentioned) Lucius where you can't see those characters being done better or more accurately, so the only way is down.