Man UTD have strengthened with Sanchez, but I don't know how he will do playing as a wing forward. At Arsenal he always seemed best being used as the lone striker, but with Lukaku leading the line for UTD he will have to adapt. It might also see UTD lose a bit of fluidity with the omission of Mata. The way we used the space left by Pogba might also be something other teams do.
Chelsea have maybe strengthened. Barkley can play in a couple of roles for them, but he hasn't played in their 343 before and Chelsea have tended to use their attackers more like wingers than midfielders. This was the biggest difference between us and them last year, where we played the same formation but Alli and Eriksen played completely differently. In this Barkley would've found a better fit with us. Giroud for Batshuayi is an upgrade though.
Arsenal are a difficult one for me. They have bought two quality players in, but how they fit with Wenger's style of play is another thing. Will he go to a 442? I don't think so, nor do I think he can incorporate both new signings and Lacazette into a functional front unit. If Abaumeyang settles early, then they will net 3 points from all of their "easy" games. However they have not addressed their back line. Xhaka isn't a holding midfielder, nor are Ramsey and Wheelchair. Elneny was bought for that job, but Wenger doesn't seem to rate him so I'd expect the better sides to still take points off them.
With Moura, we have made a noticeable upgrade. We needed an attacker, and I'm already happier knowing that we can start games with both Lamela and him on the bench. The fact that we haven't lost anyone also means that the squad is settled.
The same goes for Liverpool. VVD is a solid upgrade on their defence and even with the loss of Coutinho, they have a lethal front 3 that will consistently get goals.