You think Superman is conventionally more durable than Thanos?
I don't see Superman tanking blows from Power Gem amped Thor and doing his best troll grin with only a small spattering of blood to show for it. Or enduring a prolonged ass kicking from Odin.
The only definitive edges I'd give to Kal would be speed and reflexes, tbh. Certainly not durability.
Speed...Superman
Strength...Thanos
Durability...Thanos
Power output...Thanos
The only advantage Superman have is speed. Thanos can start this fight off with a force block...the same type of force block that was capable of holding an amped Warrior Madness Thor. Thanos is in another league than Supes or any other Herald.
Both can toss 500,000 pus ton battleships like baseballs.
Survive from huge amounts of damage.
Fly at ridiculous speeds.
Magic, and solar abilities.
Stamina greater than Atlas.
Strength that would make Hercules look like a mortal.
This all is if their powers stack, and would make him quite a bit greater than the Herald tier. Just something to think about.