I don't think European teams should be too worried about the amount of money that these Saudi clubs are willing to spend, it is not as if the European clubs are losing the best players to Saudi, most of the players moving there are either above 30 or their time in Europe was already up, players like Haaland, Mbappe, Rodri, Saka, Bellingham, etc, can never think about Saudi Arabia. Quality/high level football will remain in Europe and nothing is about to change that.
You're right. Most the players who joined Saudi clubs are the old players or the players who can't get regular position on their clubs. So, they decide to move to SPL because they can be paid with big money and can play as main players in Saudi clubs. Actually, there is nothing wrong with the players who decided moving to SPL. But European teams mustn't feel so afraid, the players who are in the ideal ages to play aren't interested to move to Saudi clubs. They must prefer to stay in Europe because the European leagues are the most competitive leagues. Players who still care about the future of their career, they must play in the top leagues. So, it is true that Saudi clubs will have no power to sign Mbappe, Haaland, Bellingham, or other top young players.
Another talk without fact, I don't believe that my friend, reason why most of those players make a move to Saudi Pro League was due to some reasons they can't control. We all have seen how Chelsea were losing throughout last season and market values comes with what you have offered from your previous club and many of them had none, if I was the Chelsea fans that made a move to Chelsea with old age, I will also do the same and retire football quietly.
Take another look at the condition of Messi and Neymar maltreatment by fans when they were in PSG, even though Messi went to US to continue his jurney to ignore Saudi Arabia, Neymar doesn't have the same power like Messi, he joined the Saudi with great contract of 2 years which is not bad, better than PSG where he had to impress and go to several injuries, he just need to focus and put small energy and make it in Saudi Arabia and AL-Hilal thus far had good players before his arrival.
In addition to how Ronaldo was threated in Manchester United when he lost his child, when he was suspended and bench by Eric, when everyone were critizing him of been stubbon but look at where he is now, where there is peace for anyone, there is going to be great achievement.