Silves doesn't really have any relevance to the economy. Basically he is an unaffordable player that will be rented out every couple weeks.
But, see, he does.
Every time he's transferred, the "agent's fees" are removed from the BB economy forever. Not counting his salary, in the past two seasons Silva is responsible for removing over $4.6 million in agent's fees from the BB economy. (Assuming an average salary of ~400k the past 2 seasons, he's removed an additional 11 million, though some of that likely comes back in the way of merch revenue, so you can ignore this parenthetical bit here.) The Polish NT center is in a similar boat, and surely there are a few more that could easily be found on the TL.
I'm pretty sure the designer's are not out of control as well. This is a strategy game and you need to make decisions. To support a player like Silves you are going to need a stockpile of money to run through while he is on the roster. If you are a growing team, it is probably best to train players within your economic means.
I agree with most of this. The undesired side-effect of players like Silva, et. al. is that as long as they're on NTs, they can't be fired. If their salaries force a team into bankruptcy, they wind up as FAs on the TL to remove more $$ from the economy.
Also, as long as players like these reign supreme as the choice for NTs, and as long as having NT players is directly related to merch revenue, there will be BB managers who continue to train giant piles of dung like Silva, and the problem exacerbates itself into a Kleenex forever.
The push to change this situation needs to come from NT managers. Yes, I'm looking at you. You are, after all, the guy who said this:
As the U21 manager, I tell people to train these huge salary bigs. As a friend advising people, I would say to train to your competition and your means and not to the U21 standards. I'd steer all my friends away from training a NT-worthy big.