Thanos fought WM Power Gem Thor.
Using High end Thor, that's 20 planet strengthx10 (WM) so 200 planet minimum. And then the unknown boost from the Power Gem. Thanos fought him head up and did well. And then trapped him in a force block.
Thanos should easily stomp here. Superman has NOWHERE near the level of strength needed to hurt Thanos significantly. Neither does Flash.
Thanos is a consistent, non-jobbing Darkseid that's still amped some with ALL of Darkseid's powers. Imagine that, remember how Pre-Crisis Darkseid stomped the JL. That's what would happen here. Maybe worse.