Look in case of Neymar, I'am actually happy there was a release clause. I think the big benefit of release clauses are to avoid situations like this with Dembele.
Barca and Neymar both agreed on the release clause, there can be no discussion of being screwed or being unreasonable, if PSG pays, he is released, simple as that. The only issue with that is how PSG financed that transaction as it wasn't really PSG that had to cough up the money but their rich owners did, from their own private pockets, which is completely against the idea of FFP. That is the issue. The reason Barca feels they are screwed by PSG is that no club could have actually paid the release clause whilst respecting FFP regulations, I mean United is one the richest clubs in the world and we could Neymar alot more than PSG but even we would never pay that for 1 player. So under FFP, that release clause protected their investment, the fact PSG triggered with outside money screwed them over and that is the point they are mad about and understandably so.
If Dortmund would have agreed a release clause of 150m, there also wouldn't be a discussion because Dembele agreed to it. But I don't think if they would have been obligated to put in that it would have been at 150m because at the time, Dembele was bought for 15m, he was a talent with everything to proof, the release clause Dembele and his agent would have agreed to would likely have been much lower, you know mostly these things are in line with the agreed upon salary. Say they would have agreed for something like 90m, as at that time Dortmund would have considered 90m more valuable than the contract they had so it was a good safeguard for their investment. Now a year later, Barca was forced to let Neymar go for 200m, they could just pay the clause and get Dembele for 90m. In my opnion those amounts and those transactions would have made sense and they would make this entire circus so much simpler.
Dortmund would have never valued Dembele at 150m a year ago, not even this year at the start of the summer. They are just using their absolute power to squeeze much more out of it than they think he is worth and the only way this is working for them is because PSG inflated the market with triggering Neymar's clause and now they are expecting Barca to cough up an inflated price because they know they can and because they know they want him alltough he ain't worth anywhere near that amount.
I absolutly hate how PSG ruined the market with their Qatar money spending spree, now all clubs have lost their senses and you just know the next time United will move in for a good talent, we will be paying the same tax Barcelona is now paying. I think that is ridiculous.