Then so be it? We cannot control how well he does or how bad he does can we?It doesn't need to play out. It's a terrible deal no matter how he does. A young, ball playing English centre back coming off a hugely successful loan spell in the Championship should NOT be sold for 1.5m. If he turns out to be good, we have no protection. No buy back clause. There's no positive prism to view this deal with.
If anything we have gotten him a decent move because it's within Prem. Yes obviously the deal could've been better, he could have been sold for lots more, but whats the point? We have brought in Laporte and Dias as our two expensive centre backs to help in long run, we have 50m John Stones sitting at the club, if we still need a Tosin to save us despite that then I'm afraid it really is all doom and gloom.
Good luck to him and I hope he proves he's a Prem level defender, but he has no future with us as of now, his value of sale becomes irrelevant because of this factor. If he becomes good and moves on then it is what it is, you cannot forsee every deal going good or bad. Plenty clubs lose players for pennies and regret them to this day, Gnabry from Arsenal to Bayern probably a good recent example, it's just how football business works. You can't win it all.