I went over the next most expensive signing that same summer in a similar position/role that wasn't to a comparably big club for our over 28 signings and got this:
Casemiro - Matheus Nunes or Amadou Onana
Varane - Gvardiol, Zouma, Tomori or Kumbulla
Cristiano - Daka or Cunha (higher fee, much lower wages)
Matic - Tielemans, Paredes, Renato Sanches,
Sanchez - Carrasco, Lucas Moura, Nicola Pepe (to Lille), Ismaila Sarr
Pretty much what you'd figure.
#8 - We're in better shape squad-wise, but production so far slightly down.
CB - Production down but not a ton because of Varane always being hurt, possibly a gem if Gvardiol would have come here instead of the Leipzig star path. Is Kumbulla any good?
#9 - We have a solid backup in place or guy to compete with Hojlund, but less production that one Cristiano season.
#6 - I think Paredes would have done okay here but frustrating at times. Tielemans same but maybe post-Fergie united we destroy an inconsistent talent like him.
W - Frustrating guys, decent talent. Carrasco would have been helpful but not a star. Lucas is done already, he was just okay. Pepe probably fails here to but you never know, he has talent. Sarr same.
We got 5-6 decent seasons out of that group of older players (Cristiano 1, Matic I'll approximate as 2, Varane let's say 1.5 and Casemiro 1 so far) out of paying them a ton in wages and an extra 10-15M or so a year in fees (big saving in midfield, medium at the rest).
Normally I'd add another 2 guys of similar quality to that group with the money saved in fees and wages, but we'd have probably qualified for less European prize money in that time and sponsorship money, so maybe that evens out, though my guess is that sponsor money is heavily impacted by being in the Champions League so maybe even a slight loss here.
So, what have we learned? I have no idea. My only real takeaways are that it's hard to sign good players, only Gvardiol seems like a real difference maker and we'd be in better shape squad-wise (maybe not financially, as probably less CL games, though maybe we make up some of that in the other 2 competitions) in the future if we'd bought younger players in the past.
Maybe the rest of you can draw some conclusions I can't see.