"Bumbling around in a Cessna doing VFR navigation has precisely zero relevance to airline flying."
I do not agree with this point, it's not necessary the flying skills, it's the experience you are faced when flying around X amount of hours in GA, real life experience when you don't have instructor in the right hand seat to guide you or take over when things go bad.
Your decision making becomes reality, not just a model that you practise and repeat again and again, until you know it by heart inside out.
There is a big difference from being alone with various factors such as weather changes, fuel, diversions etc - where not all is planned for you by Ops - where you actually have to make the decisions that might have a real impact on your life, not just you have failed a sim/training session.
90 hours total real flight time + XXX amount of hours in the sim of course. That for me can give you a good pilot on a nice day, when everything goes after plan. However I am sceptical how they will be in a real life emergency.
I can't imagine in those 90 hours, they have many hours without an instructor, have few hours solo is not going to give you much experience with real life decision making.
One of the misconceptions that some here have about P2F, is that there is no quality control of the pilots just because they have "paid their way in" - however that is not correct. Even though they P2F, they are normally put trough same training program as cadets are, and need to go trough the same hoops as everbody else has too.
For those who have done the P2F that I know about, there have many traps and dangers with this, it simple has not been easy going without any issues. And great risk is involved in it financially and the uncertainty before, during and after.
Some of them have lost much money, training has been hard they had delays for many months before completing sims, training etc.
A few I know managed to get proper jobs after this 300 - 500 hours experience. It varied a lot from what they managed to achieve, but it simply was not easy, and for some they have gained valuable life experience trough this.
For me this life experience helps develop future decision making, and is a useful for the future.
Much more then some spoiled child who gets paid everything by mummy/daddy to attend overpriced integrated flight school, who produces the next machine part for an airline!
All the ones I know from P2F, funded it themselves, in other words they did not have somebody giving them the money to do it, but worked hard and decided this is how they wanted to use their own money.
It is massively wrong for the industry, however if you want to look in these details, you must take look at many more aspects of the industry.