The idea behind FFP controls is not a bad thing.
The problem with La Liga's/Tebas idea is it's far to restrictive in it's current form. It's forcing a lot of teams here in the league to sell off their prized, talented assets for peanuts, which is hollowing out the league and making it weaker making it harder and harder for the team to reinvest into the team.
Almost feels pointless in having a release clause at this point now. No point in setting one at 20-30+ when teams in the EPL can just wait it out and force teams to sell far below it due to registration issues.
The CVC has aided clubs like Celta and Betis build spectacular new training grounds. With the space and land prices in Spain, the clubs have managed to build the best infrastructure in Europe. And that's something positive for it.
The negative is that as you suggest, Tebas has effectively made Spanish football the feeder system for the rest of Europe. No purchasing power, selling before being able to buy and low buyout clauses while transfer fees outside Europe inflate is all a snowball effect.
Lastly the cynic in me says that the name intention of the CVC was to use the mortgaging of the tv rights contracts to force Spanish clubs to have to invest in their stadium infrastructures for the world cup winning bids, rather than relying on the state to fund it.
Its well known by now that FIFA push the World Cup into countries where they get a cut on the stadiums being built.
This system with the CVC deal funding the clubs to then renovate stadia which coincidentally needs to be renovated for WC2030 is suspicious as fuck. Seems like everyone gets a cut.