I just don't really agree with assessing a squad by only looking at "3 years from now." I think it just allows you to dismiss players who are contributing now.
Since you've mentioned Real Madrid a few times: we sold Varane to United and then signed Alaba and Rudiger. Both of them are older than Varane. They will probably not be around in three years. Neither will Nacho, who is 33. Carvajal and Vazquez, the two right-backs, are 30+ and also won't be around. At left-back, Mendy is 28 and unlikely to get a renewal offer, so he probably won't be around in three years either.
Does this make Real Madrid's defense "not fit for purpose"? Is it a "terrible" defensive squad? I don't think so. They are players who can perform now. They will be slowly replaced in one, two, three, four, five years. Some will take different roles (no longer starters). Some might be replaced by comparable free agents (as what happened with Varane).
Varane, Casemiro, Reguilón (who all played at Real Madrid), Eriksen, Mount, Rashford, Hojlund, Fernandes, Martinez. I would hesitate to take "lower tier" English players, mostly for nationality, same as you might hesitate to take Fran García, Nacho, Vazquez, etc.