Swansea? He was fantastic actually, but as part of a really good defensive unit. His performances on loan were what condemned the club to sell Tomori. Guehi was always highly rated internally but the main concerns were his height (he is "only" 6ft) and pace, which stood out like a sore thumb in comparison to the visibly more athletic Chalobah and Tomori, both of whom could also play multiple positions in defence. Colwill had also just broken through, and for obvious reasons is the most highly-rated defender to come out of Cobham since Reece James.
There was no way that Guehi could be anything other than 4th choice rotation behind Christensen, Rudiger and Silva although he would have got a lot of minutes thanks to Tuchel's preferred back 3.
The other issue was the FFP pressure of the Lukaku purchase (FFS) so when Palace came offering 18m pure profit + a buyback clause, it seemed to be a mutually beneficial offer.