I think this is a good concept, but like all games, it just succumbs to exploiting imbalances. In Football Manager, its just finding all the Uber Wunderkids who can easily be bought for less than the lowest rated players in their prime. Then you just invest all of your money in coaching/facilities who can also be bought for significantly cheaper than adult players and in a few years, once the players hit like 18-19, you have a world class team that only continues to improve as they reach 25-26. Give it 5-6 years and your team is like a team of Ronaldos and Messi's at every position.
Presumably the unrealistic part is the how well it is possible to predict who will excel to a world class level.
You take base athleticism and technical ability and you can clearly produce national league quality players very predictably and consistently. One would assume it is more difficult to judge future world-class potential and even more so the likelihood that potential will be lived up to.
Some of them sort of do or are trying to do this already.
Arsenal actually bought StatDNA, a football data analytics company, a couple of years ago. So time will tell how they will use this to their advantage.
In real life, "finding all the Uber Wunderkids who can easily be bought" is actually extremely hard, as there are too many external factors that could determine if a wunderkid becomes a Ronaldo, as demonstrated by several talented athletes that achieved nothing.
Plus, a lot of those factors are hard for an algorithm to "handle", e.g. luck in finding/identifying a wunderkid, getting him motivated and committed, him having enough maturity to work on improving and the psychological resilience to withstand what comes with the job, etc etc...
What are the odds any football team would produce a single Ronaldo or Messi from a youth prospect? What are the odds they would produce a team full of them at every position?