Honestly, I would have to guess that right now, the Su-27S, or other limited upgrade version, (not the heavily upgraded versions like the Su-35, or SU-37) is about equal to an F-15 or an F-18.
Fact is that we wouldn't be facing swarms of these upgraded Su-27MK2's, or Su-30's, we'd be facing swarms of the Su-27MK, Su-27MK3, and other rather less impressive fighters.