1) Every team replaces its staff once in a (short) while.
They do that for saving few thousands in his contract time.
They will surely will like to save some tens of thousands by that.
2) I guess that the fact that for hundred of years ALL thought that the hearth is flat proves (upon your claim above) that the hearth is flat and not round (as no one exploited that until...)
3) Signing bonus? does not exist.
Firing payment exists, but it also exists in case you just replacing your staff which all does anyhow, once in a (short) while.
Perhaps for (1) and (3) you are forgetting that to get a replacement staff member, you have to bid on them. And while at a point in a staff member's career replacing them becomes a good decision, that is a factor of what his salary is and what the replacement will cost. If you have a level 5 trainer with any reasonable salary, for example, firing him to save two weeks of salary is foolhardy since it'll cost you upwards of 5 times that salary to acquire a similar replacement.
As already stated at the beginning of this suggestion, this is something they will need to calculate when doing that.
But, due to the fact that this means tens of thousands of profit it will be a (very) big factor of which staff member to choose, as this firing will be profitable, and it will still lead to this firing action.
For (2), you can point to data that proves the world is not flat, which directly contradicts the theory. As I have shown you, the rules in this game state one thing and the game is programmed in a manner that bears that out explicitly and correctly. If I say the world is round, and the data shows the world is round, but you think that a toroid-shaped world would give us more land to farm, your belief doesn't mean that there is a bug with the world or the data.
Again - the game document is not the fact, as the maps at the time of Galileo had not been a fact.
They only had been a fact of what people thought and not that their understanding was right.
And again, free salary for staff in the offseason can directly lead to exploits allowing people to train with level 7 trainers, a far more realistic scenario with far more imbalancing effects than your mass staff hiring/firing parties could ever have. You know, if you care about the game and balance and all that, think about it for a second or two.
I could write a lot about it and prove it is a wrong claim, but instead I will add another limitation that will turn the table - staff member cannot be fired or replaced in less than three weeks (for example).
Good enough for sealing this non-existent hole.