we could have had an updated and enhanced fleet of TriStar tankers
No you couldn't, because 6 Tristars did not, could not and cannot meet the UK requirement for AAR!!
It really is that simple.
As for the USAF and their KC135s and KC10s, well the USAF tried to ditch the latter just last year and the former will all be going under KC-X, KC-Y and KC-Z programmes. You have heard of these, haven't you? Of course the USAF need new tankers and they are planning to get some!!
As for Tristar v FSTA, well I suppose the Tristar did have an air eng!!
