I understand what you're saying, and I agree, mostly. Basically, I'm suggesting that transfer windows only be used to limit the times when the players can actually transfer (move themselves from one club to another). Nothing else need change. In the real world, transfer fees are usually paid when a contract is signed, which may happen long before the player actually packs up and moves.
Nope, you got it wrong......
I am saying that, despite other managers, GKO unlimited transfer system is OK, because the game has so many things that makes a each player totally different and some tweaks that the game can fit for every kind of manager.
* If you don't like buy and sell players all the time, you've a decent squad, that can beat any player if you make things right, most of your players has at least CA3, decent experience but most of your players lack progression potential, you'll be fine a couple of seasons, and eventally you'll realize that something needs to change in your squad, because your players won't have anything else to offer.
* If you like to improve your squad, it's ok, you can sell those unused players and buy a couple, things will go well once your player is adaptated to your squad, it might happen in a couple of weeks or take you some months, each player is different. You might consider adaptation to the team a penalty for those to buy new players all the time, if you change half a squad you'll be doomed, everything must be slow.
* Finally, those who like to make teams from scratch, promoting youth players and making them grow. It might sound strange to you, but with a limit in transfer market promoting players would be almost impossible or take a couple of years in real life! Why do i say that? Because even if you want to make a youth team you need money, lots of money!
In previous cases it was a bit unnecessary improve your training facilities a couple of levels, because most of your generated players at the beginning doesn't have much to improve, however, youth players has quite low current ability and, in order to make them strong faster, you need to upgrade you training facilities and get better coaches, else, your youth players doesn't have any chance.
I'm not saying this without notice,
look at my squad, you'll see a team based in youth players development (my squad's average age is 20.1), doing someting like this in less than 4 months would be impossible if i were allowed to buy and sell players just a couple of weeks every season, believe it or not,
buying a player at low cost and sell them to get some profit is the only way this could be achieved, i believe activity in transfer market is one of the few things that can make a real difference between active managers and those who doesn't play often, if we lock transfer market..... well, i should log only once per day, make some club activity and that's all, but my team's improvement will be frozen, i'm sure of it.