I don't think it's correct to say that this has been done to stop players exploiting the market. The changes have been made to reflect what's happening IRL.
I have made an effort to dig into the data to show that it's rare for a South American 16yo to move to Europe and by doing it, I've also increased my knowledge in this area. I have also posted why 16yo South American players transferring to England will be very rare, if there will be any. So far, I haven't seen any data from the other side of the debate to show that the changes are unrealistic.
Users in this thread posted that they are able to sign 16yo players from within Europe as another EU team and that is happening IRL too.
So far, it doesn't seem like anything is unrealistic in FM23. If that statement isn't correct, then I really would love to be corrected with factual, recent data. I haven't delved into every transfer that happened recently, so it is possible. Man City and Real Madrid were brought up and I checked it out, along with also checking Barcelona.
As for the list of footballers posted:
Garnacho - was born in Spain, has Spanish citizenship and was in the Atletico youth team.
Hannibal - Born in France, has French citizenship and started off in the Paris FC youth team.
Adam Aznou - from what I can see, born in Morocco, has Spanish citizenship and started at the Barcelona youth team.
These transfers could still happen (EU to EU), based on a couple of users' feedback in this thread. The complaint seemed to be about South American 16yo players though?
Vininistus Junior - as mentioned before - the deal was done in 2017, 5 years ago.
Jude Bellingham - was 17 when he transferred and correct me if I'm wrong, but I don't think the Brexit rules were in effect back then. It is now, as I have posted earlier in the thread.
Gabriel Martinelli - was 18 when he transferred. That's possible in FM as well.
Cesc Fabregas - I don't know why he's on the list. He's Spanish. He did leave Barcelona at 16 to join Arsenal when England was still part of the EU.