They are outdated. Their huge rcs makes it an easy target for any new fighter.
RCS is not as important as many people seem to think...
First of all with new carriers with AWACS platforms onboard then nothing reduces RCS like not having to use your own radar.
Another aspect is that aircraft never operate alone so one aircraft could be blasing away with a huge powerful radar scanning for targets but passing on that information to 5 other aircraft in the formation... the enemy will see the active aircraft, but how will they know there are five other aircraft there?
The Su-30M programme actually intended the Su-30M to operate its radar and search for targets in a mini AWACS role controlling a flight of smaller lighter cheaper aircraft that would close with the enemy position radar and radio silent to launch missiles and then withdraw... an enemy would detect the Su-30M some distance away and then all of a sudden missiles suddenly appear close by with lots of energy because they haven't flown 100km from the Su-30M, they flew 30km from the MiG-29SMT... so you are well inside their no escape zone...
Equally future advances in radar technology... if claims made today are to be believed, suggest stealth is not going to be that useful in the future with radars becoming rather more effective instruments than they are today.
You are not seeing Almaz Antei complaining about Russia selling S-400s to Turkey because Turkey is getting F-35s, but you do see the Americans jumping up and down because Turkey is buying S-400s... are they afraid that their claims of stealth might not measure up to reality?
Perhaps American F-35s are going to be stealthy but models sold to international partners wont be and that is the secret they want to hide?
Either way a nice big Flanker should be able to carry a rather large powerful radar... if they are not that stealthy anyway they wont mind using it and detected enemy platforms in view... if they were highly stealthy they would avoid trying to use their radar for fear of giving away their location.
Of course the Su-33 should be able to carry the external targeting pod carried by the PAK FA which should allow passive targeting on the cheap too.