Not sure self-righteous condescension and snootily labeling people "armchair general" is the best opening sentence to a thread.
Anway, since the Barcelona example was used - to fully appreciate their success you have to consider the bigger picture and go all the way back to Cruyff's tenure, and his emphasis on totaalvoetbal as a cornerstone for the academy which had a trickle down effect after almost a decade. The likes of Messi, Xavi, Puyol, Iniesta, Cesc, Pique etc are the results of careful planning, and didn't just crop up overnight. We can't arbitrarily pluck this moment in time to further the argument. They produced major talents later on, but in the beginning the most decisive pieces for Cruyff's Barcelona (the spiritual ancestors of the current side) were the likes of Laudrup (one of the greatest #10s of all time - bought from Juventus), Romario (one of the greatest strikers of all time - bought from PSV Eindhoven), Ronald Koeman (one of the best defenders of the past 25 years - bought from PSV Eindhoven), Hristo Stochkov (one of the best strikers of the 90s - bought from Sofia), Miguel Nadal (bought from Espanyol) etc. for large amounts of money. One could argue that United doesn't have players of that caliber to be the building block of things to come.
You need a nucleus to build the team around first, and then start developing players, as Barcelona's history shows. Patience is a great virtue but you need the raw materials to mold. You look at our defense - and the have major problems staying fit - not a great starting place if you can't consistently rely on them, especially once get European football and the margins for error are reduced to a 10th. Our strikers are ageing, and the midfield seemingly crumbles without Carrick. That has to be addressed pronto with top notch additions. Since we don't have a good enough foundation right now, the squad has to fortified with quality players bought for large transfer fee. Also it's easy to forget, but Barcelona had a 6 year barren spell from the late 90s where they won nothing of substance. Until the arrival of the likes of Ronaldino, Eto'o, Davids (from other clubs) that is.
The motto "great teams are built, not bought" is great in theory but doesn't always translate in practice. If it was so simple to build great sides everyone would be doing so instead of hemorrhaging revenue on transfers. Ajax would still be developing Cruyff and Neeskens and Krol and Keizer; or Van der Sar and Seedorf and Kluivert - and dominating Europe. But they aren't because these things go on cycles and relying on an outdated notion will only set you back, as teams like them found out the hard wau. United could have a good core of academy players thus reducing the need for imports, but it will be a very long term project and until then it's imperative that we plug major deficiencies in the starting XI/ the squad in general. Objectively speaking we need to tweak the academy and the results will only be evident in 7-8 years at the very least. And even then, the mathematical odds are against a glut of high quality starters. Even Barcelona haven't produced players of significance since the emergence of Busquets and Thiago almost half a decade ago and have spent Top-5 all time transfer money on two separate players in consecutive windows.