well f35 looks fat and clumsy like average American .they paid more attention on stealth than aerodynamics .
In order to understand Su-57 or F-35 we have to see their needs and niche.
For Russia, the ICBMs, SLBM and submarines and hypersonic weapons are priority, it does not matter China or the USA build more weapons, Russia just needs the one that assure these rivals will be highly mauled if they attack Russia.
PAKFA Su-57 is not that type of weapon, it is a tactical fighter, it is more to export and make money, why? well the USAF is an imperial air force to be used on weak nations.
F-35 has to deal with Su-30s or MiG-29s and S-300s or S-400s, so Russia designed the Su-57 as counterpart, pretty much Su-35 can deal with such threads, but it is getting old, so Su-57 assures export market share in conflicts like India had with Pakistan or Syria has now, and potentially Iran or Venezuela can have.
F-35 is basically built thinking Russia or China do not have real counterparts to sell to nations like Iran, Su-35 while it is a good aircraft, well it is an old platform first flown in 1977 and 1981.
J-10 is old a JAS-39 gripen type of thread, J-11 despite all the fanfair is old too, not better than the old F-15 and not a high performance aircraft like Rafale or Eurofighter.
F-35 is an attack aircraft, but really ill suited for replace the A-10, A-10 is a flying tank, so well it will not really be better it is too delicate, the F-16 is a better dogfighter in general terms and Su-35 is even better same Rafale.
F-35 is an stealth attack aircraft, Su-57 its main export rival to intercept it and down it.
J-31 is a copy of F-35 but much more limited than F-35 and J-20 too big to win the export market, Su-57 does not fill well its niche, because the engine is the main concern of Russia once they have something like f135, they will be able to make a F-35 type fighter to compete with it, J-31 might eventually compete but its size limit makes it less capable as dogfighter and it repeats the mistakes of F-35 with even more limited engines.
So F-35 indeed is a good export tool, Su-35, Su-57 or J-20 can not compete in reality, Russia will need a right engine and make a single engined fighter to compete or make their UCAV a machine to partially deal with F-35.