You're entitled to your opinion mate, but you're looking at it in a very pessimistic light. I agree with some of your concerns in general, but I'm also open minded about how it could work. You also have to bear in mind that the midfield only started to look a bit ragged after an incredibly draining run of games brought on by our Europa run and the winter WC. We don't have to contend with either of those things next season.
Casemiro's form also dipped because he missed so many games in quick succession due to suspension. I know he's getting on a bit, but there's no reason to think he'll drop off a cliff that much. He had to contribute to our attack a lot as well last season, so having a more mobile and attack minded #8 might allow him to focus more on just shielding the defense and conserve some of his energy.
Judging by the type of GKs and defenders EtH has targeted, it's obvious he wants us to dominate and control games more. This in itself should take a lot of the pressure off of our defenders, if he can get what he needs and implement it effectively. Unfortunately, he can't just revamp every part of the team that needs it in one window like Pep is able to do at City. He has to make moves towards that vision, whilst also accepting he'll have to make do with areas as they are, like our RB situation.
You also need to stop comparing the side to all these other teams. It's likely what we'll see will be entirely different. We have no idea how he'll utilise Mount yet, most people are just making educated guesses, but you don't need to write it off so hard before a ball has even be kicked.