I'd say between him, Potter and Poch, Maresca is walking into the most settled situation. He won't (I hope?) have to oversee a huge overhaul in the squad this summer and the group he has at his disposal is a group that have now been together for a little while. The players in the squad have been trickling in over the last 18 months - Enzo, Mudryk 18 months ago, Caicedo, Nkunku, Palmer, Jackson 12 months ago. So it's kind of a settled squad now.
It's a challenge of course, and you're right expectations now should be to improve on Poch's work. At least that's my expectations. He has to get top 4 minimum. Some might say that's a tall order, and unfair to lump that on a novice like Maresca but he's taken the job, the team finished 6th last season (one swing result away from 4th place, I might add) and the squad will remain relatively the same, so we can't go back to just hoping for top 6 again.
If he thinks he can't find the right set up for none of Enzo, Mudryk and Nkunku then there's already a problem with the coach. It's fair enough if Enzo was the odd man out in Maresca's midfield, or if there was no space for Mudryk in the attack, but 3 big money signings? That would be unacceptable. One, maybe but three? Perez wouldn't accept a coach walking into Madrid and deeming Alphonso Davies, Camavinga and Bellingham unfit for his system for example. The coach would be asked to make it work and I think that would be a fair standard to set.
I think between Maresca, McKenna and Thomas Frank, I'd have preferred Maresca but truthfully speaking, he's a complete novice and his biggest challenge will be getting the players to buy what he's selling and getting the fans onside.