There's a huge difference between a team that is world class in hindsight and a team that is bought to be world class.
You look at our world class 2008 team and who was brought in as world class... VDS, Evra, Vidic, Park, Nani, O'Shea, Fletcher, Ronaldo, Tevez, Anderson, Berbatov, Carrick, Hargreaves, Brown... none were world class.
World class is usually defined by achievements, which in turn is usually defined by great teams coming together under good managers. Over the last decade we've had 4 truly great teams in United, Barcelona, Bayern & Real.
How many of those teams have been "built" as world class? Real possibly?
The model of "world class teams dominate" so buy world class playera is great... Except reality shows that a great team creates great players, not the other way around.
Dortmund & Monaco are prime examples. Their players aren't all world class, but the sum of all parts is greater than the individuals. That was always the case with Fergie... Put Vidic in Wengers back 4 and he may well look like a donkey. Put Park in Chelsea's squad and he may have never played.
I'd love to sign Sanchez but I'd prefer us to be looking at our squad in 8 years and saying "of course we won 4 PL titles, 2 CLs, 3 FA Cups and 2 League Cups... We had Martial, Mata, Mkhitaryan, Rashford, Pogba, DDG, Bailly, Jones, Herrera, Shaw, X and Y... World class players make a world class team".
That's on Jose.