Southamptons director of football used to be head of City's Academy, it's no wonder that a) they are picking up City's best products and b) there's a slight over inflation in price as City know the knowledge of these players is high and so know how highly rated they are.
I’m aware they have their former DoF, however, I can’t imagine that means much at all in reality. Every top club would, or certainly should, be aware of seemingly world class talent playing in City’s reserves. In fact, they probably knew about them for several years. United, for example, sign young players without first team experience from clubs in Norway, Spain and beyond. The talent of City products would not be an unknown to them, or to West Ham, Everton, Brighton and more.
City are continuously flogging them for inflated fees to just one club. I think Southampton only just broke their transfer record in January to sign Suleimana from Rennes, and that was only 25m. Some of these kids aren’t far off their most expensive signings ever. They seem to be doing City a favour. I have no issue with them signing familiar players, but the fees are certainly above market rate. Especially as they seem to contain further clauses, certainly in Lavia’s case.