Replacing the goalkeeper with another good one isn't going to make them much worse. Sarri will properly not bother too much with EL football, just like he did with Napoli, and Kovacic, Jorginho and Kante is an incredible midfield which is far more likely to change things than them switching a keeper. Conte and Guardiola, the last two premier league winning managers, 'had no prem experience'. And yes, they would both walk in to our midfield, Jorginho was one of the best midfielders in Serie A last season for a team which pushed Juventus for the title, and Kovacic is a class act. We currently field Dier in there, an injury prone/declining Dembele, Wanyama and a returning from injury Winks.
They finished above us last season because they added Matic and Lukaku. Those two players put them above us, they improved them and (shock horror) that made a difference as they collected more points. This season we've signed nobody and they brought in Fred and Dalot, so even if those two do nothing they're still a better side. Of course there's a chance we could be better, but it's based on nothing but hope because we haven't changed at all. United fans are annoyed at their window despite having a much deeper squad and also signing two players .. we are unique in doing nothing.
We're more a massive disappointment than a disaster. Had an opportunity to improve on things and freshen up the squad ready for the new stadium and didn't take it. Sure we 'might' improve and magically things 'might' get better, but we're relying now on good luck and hope, rather than actually trying to address our issues. That's a terrible strategy.