Sanchez and Alli are 22, Dier 24, Kane 25, Davies 25, Aurier 25, Eriksen 26 and Son 26. Any of them can get better. Only Eriksen and Son have entered their prime but at 26 they can improve further. These are 8 first teamers, 6 of them 25 y.o. or younger.
Why are they going to feel better at their stadium than at Wembley? Well, it's not rocket science.
Dier, Alli, Davies and Aurier have shown no signs of improving. Sanchez would only pay instead of one of teir other centrebacks who are significant;y better than him (one of who they might yet lose anyway). Kane and Eriksen are already their two best players and Son isn't really that good and isn't available to them for at least part of the season anyway. You don't get anywhere by changing nothing.
This argument is also self defeating since all the whining on here is based on us not signing anyone and therefore not improving. Except we actually have signed someone. We also have players in the same age bracket as above who you can apply the exact same logic to. Rashford, Martial, Lingard, Pogba, Lukaku, Shaw, Bailly, Fred, etc. So again, explain how this argument ONLY applies to Tottenham? Did they not finish comfortably below us last season?
If it's not rockket science why can't you answer it?
There is no reason to logically think Spurs will do better than last season or that United will be significantly worse. Liverpool have signed half a team so you would expect something different. CHelsea and Arsenall have new managers so again there's an unknown element. Spurs are exactly the same and United have not made significannt changes one way or the other. If you stay still you generally can be expected to stay still unless others overtake you.