If they forked some of it off from GTS then it's not a ground up rebuild, the degree of missing features and poor netcode is also worse than the most compariable titl ein your list, which is Forza.
Nor does, to be 100% clear, whataboutism excuse the state than GT7's on-line is in.
And who set those priorities? That would be PD, as such they are responsible for the issues, and the current state of the title, and that's the state it will be judged on. where it is now.
To use a direct example, I was a massive BF player, had been for years, but I'm not going to give BF2042 a pass because of what it might become. I judge it on the spectacular mess it is right now, I don't point to other titles and say 'well they messed up a bit as well'. No, I hold the developer/publisher to account for the utter mess they created, and I see no reason not to do the same with PD/Sony with regard to GT7.
Let's also be clear that your claim was "online which is hard to test remotely", which is, to be blunt, utter nonsense. Quite the opposite is true, local testing of on-line is the wrong way to go about it, as it will give you far more false-positives than large-scale remote testing will ever give you.
To be 100% clear I was a public beta tester, so not employed by Sony and not paid. I did it because I love video games. Sony ran the programme for over a decade (PS3 through to PS4), and you had to be active it both signing up to tests and providing feedback to stay on the programme.