But it was announced also that a multiskilled player with balanced skills would train faster than a monoskilled player and it's not the case.
No, it would be stupid. I belive monoskilled player train slower only the highest skills. It's only reasonable conclusion about elastic effect.
I explain it by example.
Please consider two players:
order of skills: JS JR OD HN DV PS IS ID RB SB (but it doesn't matter):
player A: 3 3 3 3 3 3 3 19 3 1
player B: 10 10 10 10 10 10 10 13 10 7
and it works in this way:
ID=19 of player A trains slower than ID=15 of player B
but
SB=1 of player A trains faster than SB=5 of player B.
It happens because if player A trains ID then only 60% of training goes to ID but 40% of training goes to SB whilst if player B trains ID then 85% of training goes to ID but only 15% goes to SB.
However if player A trains SB than 99% of training goes to SB and only 1% goes to ID whilst if player B trains SB then 91% of training goes to SB and 9% of training goes to ID.
In this way it's easier to create multiskilled players and harder to create monoskilled players.