Kasparov is the highest rated player. Deal with it.
So because it's not FIDE, your assertion is that somehow it's not legitimate?
Don't take my work for it, go ask FIDE and Ruslan Ponomariov.
Krammnik was in his late teens when he lost many of those matches, and Krasparov was in his prime.
OK, following your logic, Kramnik is the one now in his prime and Kasparov is not. Therefore, Kramnik should now be dominating Kasparov, but he is not-- neither in terms of rating (which is a measure of playing strength) nor in terms of games against Garry.
Whatever. Hopefully we will see a re-unification match (which all three parties, Ponomariov, Kramnik and Kasparov have already committed to) and the question of who is the real world champion will be decided.
I'd like to see that. Who do you think would (or will) win?