I would think two or three could have some chance, given that giant robot Ultron seemed to be too much for herald levelers without the Quantum Band soul strike.
A KO? What you're saying ignores the Durability that Thanos has shown time and time again. I mean being giant sized doesn't secure a victory in all cases.
Is the Quantum strike more powerful than what Thanos has shown to let off (energy wise) in the past? Who's the better tactician in a battle? Can they hurt each-other?
Thanos in his self titled quest was able to resist reality warp, entropy, physical degradation, the list goes on and on. I can't be completely certain, but it seems to trump being assimilated by the Phallanx.
Just look what happened when they tried it on Wraith, if he can resist and punish them at their own game, Thanos being what he is may be even worse for them (assimilation wise).
Ultron can kill top tiers, and while Thanos is certainly stronger than any opponent he has faced, he won't be fighting back. Thanos can be hurt, Ultron can attack body and mind at the same time relentlessly.
Given that Wolverine level adamantium with Wolverine level strentgh has passed through Thanos I don't see any issue here
But seriously, I'm just saying Ultron has some power to work with here.
Everything that you mentioned about Ultron can be applied to Thanos as well. Which is why I asked if they could even hurt each other. The Wolverine slash was back in the day, current Thanos' skin shattered Gamora's G-Slayer, and left no marks on his skin. Thanos also possesses a trump card called mysticism.
You can't use Drax in this scenario, it's like saying that because a guy made of kryptonite could kill Superman means that the same guy could kill Wonder Woman. Drax is Thanos' kryptonite, or at least he was... not too sure these days, Thanos has changed.
After coming back from his death Thanos was indestructible, after being zapped with the Cosmic Cube he got back slowly to classic levels. Assuming Thanos make it pass the first 30 minutes, does he have any magic feats to deal with Ultron? Specially since he developed forcefields that blocked SW's attempts to affect his internal structure.
Good questions, and valid points, I guess we'll have to fall back, and find out just how powerful the Titan has become. Just remember that Thanos is the Avatar of Death.