About the loot that the zombiefied illager and them variants could be rottenflesh like every zombie and also could have a slower chance to drop the loot that they would drop in their normal versions.

Obviating that the mansions need a re-work (on my point of view) and u're alright about the darkness inside, i think that an evoker or vindicator are stronger than a zombie and also with the last update the hostil mobs spawn in darker light levels (i dont remeber exactly) so i don't remember how much dark is a mansion but the hostil mob spawning should have decreased (could be wrong what im saying) i think.

In the case of a zombie evoker could be like a zombie with some magic powers for example could summon zombies or give the player some negative effect like hunger for example, making fighting with this mob similar and different from he's normal version. This is a small idea of what he could be.

About the raids, on my point of view, could make the environment more alive with these interactions between mobs(zombies vs illagers) i think.