why there won't be any farms, when NT prospect only get cheaper but are still needed?
I don't think understand what you're asking here. Farm teams would still exist, but not because of this proposal. The national teams would need players the same way they always have. I guess the only effect on the NT would be managers caring less about drafted/NT available players, and more about created/unavailable players. I'll grant you that is a possibility.
And those dude you proposed goes around 1,5+M at the beginning of the next season when he is 18, ok maybe different when everybody have it but this would make draft investment even more stupid since it is already hard to get the money back today.
Fine. Make it more expensive. Make it cost 1.5M to create a player. And if we're worried about it effecting the draft system (that no one likes anyway) let's fix the draft system so managers have more control over it. That's a different thread though.
My point is that an addition like this might be able to work without negatively effecting all that much. If the cost is enough, then not everyone will want to do it (you can invest a lot less than 1.5M into the draft and get a better prospect than what I wrote). But if it the cost has the right balance, I think it'd be a very marketable aspect to the game.