Su57 might be a subpar 5th gen, but so is J20. Stealth is not the beall
This sentence seems to be the fundamental problem with your description of the situation.....
Yes, stealth is such a ludicrous advantage that not having it is suicidal vs an opponent that does. It
is the be all and end all in modern air combat.
Pakistan's problem, is that unlike china, it cannot have a fleet of 5th gen - Even their own analysis doesnt go beyond two squadrons, which would provide little to no resistance if Indian ground based missile systems are adequately developed to deny airfield operations.
Regarding the "parallel" drawn between J20 and Su57, it is completely wrong. Su57 stealth is just better than Rafale in clean configuration. OTOH, J20 is just slightly worse than F35. Is J-20 without issues? Not at all. But to pretend that it is not an issue for us is a Paki level delusion we should not fall to.
Like the ex ACM said, I think we should push for MUMT drones while expanding missile numbers, and wait till AMCA. For a while, the chinese will also not be able to wield all their 5th gen planes against us, they just dont have the numbers on their side for a realistic 24/7 CAP over sino Indian border. (shiv had a vid calculating this iirc). Till the time they develop that, we could sort out our stealth fighter.
But if you cant wait, or dont want risk, go for F35. IMO ideal scenario would be
leasing 2-3 sqn F35s for 10-15 years, but IDTS thats an option, so buying is not irrational.