How can Thanos even compete without the IG?
(Inset T-vo comment about how Superman can take the IG with T-vo, thanks to the misinformation about how T-vo actually works.. Seriously, all it does is alter Supermans state of consciousness from Beta to a dream like Theta, as Dominus can only tap into his thoughts on the conscious beta wave to alter reality, and somehow it's accepted that T-vo lets Supes battle with reality warpers!)
If this is Morrison Superman Prime, than honestly he has few feats..
If it's Johns Superboy Prime, Thanos should be able to turtle up in his force field and exploit a weakness. (If his raw durability can withstand attacks from Tyrant or Odin, he can certainly survive a Superboy Prime speed blitz and put up his shields, or end the fight by s transmuting him like he did a Skrull, or mind blasting him, or containing him in one of those stasis cubes he tried using on Odin...)