That’s for the teams/players and authorities to decide but every player should have a release clause that is not as ridiculous as the Madrid ones.
With the amount of real time statistics going around it wouldn’t be hard to factor in market relationships for players of similar position and quality based on historical (inflation adjusted) sale patterns.
For example if Neymar is sold for 200 Million. Messi’s release clause cannot be 700 Million because he is not worth 500 Million more based on performances and age.
Madrid's buyout clauses are ridiculous, no argument here. Don't know how they do this but I wouldn't be surprised if they pay their players (especially those on relatively low wages with high clauses) a lot of money under the table to sign those kind of contracts.
I don't think release clauses for all players would actually solve something. In opposite, I think La Liga should also get rid off those clauses because they are harming their clubs comparing to other top leagues who have no such obligatory clauses. Not only Barça but especially smaller teams with not as much financial power who have lost tons of talents over the years for basically nothing. These clauses are based on some 30 years old legislation and let's just say a lot has changed since 1985. But I don't expect they'll do something about that, it's Spain after all we're talking about.
But for arguments sake let's assume that your proposal could work and FIFA/UEFA would instruct clubs to insert release clauses in players contracts based on their market value. Sites like Forbes or Transfermarkt already have mechanisms to calculate those so that wouldn't be a problem though it's questionable how realistic their estimations are. The problem I see here is that often "true value/importance" of the player for his club will fairly exceed his "market value".
Let's take for example Puyol. There were other times on the market when he was still active but I don't know if his market value even in his prime ever was higher than 30M. He was a defender and not very marketable. But his true value for the club was much much higher because of his other qualities like leadership that can't really be measured with any statistics. So let's assume that his clause would be set at around 30M and he would decide to leave one day but the club wouldn't want to let him go just yet. Would we be happy with only getting 30M when we valued him higher?
Another example: Inaki Williams. He's playing for one of the historically biggest clubs in La Liga who have slowly lost step with other big clubs over the last 2-3 decades but they are still considered much bigger club than for example Alaves, Celta or Levante who will (most likely) all finish ahead of them this season. I'm mentioning this because club's name influence on players value, in other words, value of the players in bigger/more recognizable clubs could be higher for 10 or 20 millions compared to the players in smaller clubs with less media coverage even if there is not as much difference in their talent level.
According to TM Williams market value is 30M. He has signed a new contract until 2025 with 80M buy out clause which can go up to 100-110M over the next few years IIRC. So what's his true value in this market? 30M? 60M? 80M? 100M? 10 or more clubs could pay 30M for a player with his talent and few clubs could go up to 60 or maybe even 80M. Don't see anyone paying 100M right now but could easily happen if he'll continue to develop in 2 or 3 years. But what is Williams's true value for Bilbao? I would say he's indispensable for them the same way Messi is to Barça. Obviously we can't compare their talent/quality level but even if Bilbao would get 100M for Inaki they would face the same dilemma we would if we'd get 300M or even 700M for Messi. How to replace him? In a limited Basque pool talent replacing Williams would probably become equally tough or almost impossible for them than finding Messi's replacement anywhere in the world for us. I don't know if Bilbao would accept 60 or 80M for Inaki if he wouldn't have buyout/release clause but I'm sure that in case they would have to sell they would prefer to get twice or maybe three times as much than what his probably calculated market set release clause would get them.
Another example could be younger players whose value often can explode exponentially in few months. Like for example Loren Moron. 4 months ago almost nobody knew about him, now his value has increased for 10-15 times so his release clause would be around 8M I guess. But why should Betis sell him for »only« 8M if they can keep him for another season and hope he'll continue to develop and they can possibly sell for 15, 25M or even more?
I also don't know how injuries would influence on players value. Let's imagine this situation. We have a player X who has just signed a 2 year contract with his new team. He's 25 and entering his prime years but has so far played most of his career in lower/inferior leagues where his new team discovered him and were impressed enough to pay 3M (which is a lot for a club of their stature) so that's what his real time value would be at the start of the season. Then a team that was expected to finish midtable or even battle against the relegation is suddenly having a great season and are pushing to finish in European competition and that player X is the main reason for their success. Because of his great performances his value has already rised up to 10M and could go to 15M or more if he'd continue to play on the same level and his team would finish in top 6. Not suprising, bigger clubs have already started to show interest to sign him and it's all but decided he'll leave at the end of the season. Then, 2 months before the season ends that player tore his ACL and is out for 6 months. What is his real time value then? 3M, 6M, 10M or possibly 15M? Many clubs would take a risk and sign him for 3-5M even if it would be possible he's just a one season wonder and/or will never fully recover from injury. But is it fair that his current team where he made his name on the "big stage" would get 2-3-4-5-times less than what they eventually could if he wouldn't get injured but he'd have no release clause so his club could ask for more (negotiate with interested clubs) or just decide to keep him?
Just some examples of the problems I think could emerge if clubs and players would be pushed to insert release clauses into their contracts from third parties (FIFA/UEFA). So I don't think getting obligatory release clauses into every player contract is a solution. Instead I'd suggest players/agents to negotiate short-term deals when they first sign with new clubs. Let's sign 3 year contracts instead of 5 years and you can add clauses that contract is automatically extended for another season or two if a player has played certain number/% of games in his last season etc. If both sides are happy you can always negotiate a new longterm contract but if one or both sides are unhappy it's easier to get out of shorter contracts.
