I never really did like the seedrians, as I figured Sonic X would have a proper closure once Sonic and co. were sent back to their homeworld, despite some screw-ups along the way (I DID like some moments in the anime, tbh) and how Chris was written, it could've been a relief.. until Cosmo came along and I'll have to put up with one more season of this, which I gave up on after it. Sonic X's opening theme at that point would've been Makenai Ai ga Kitto Aru at that point for obvious reasons. And how their race works makes no sense to me. If the females were to get attacked, males turn into metarex to protect them and then die. Yeah, great survival stradegy as once they find the females, the race is pretty much screwed. And apparently they turn into talking trees if they live long enough, which makes no sense. And eggman of all people ejects chris into space in the end.
TL;DR: The last season made no sense.