| > I also think Thanos' durability was because Death never allowed him to die, but as soon as she was willing, a top tier punched through his chest rather easily. |
It was more complex than that, Drax had been created by a semi-abstract called Chronos and bio-engineered to be able to cut thru Thanos defences and do the deed.... Maybe at that point Thanos & Death had agreed it was time for him to die but the build up indicated it was purely because Drax was now powerful enough to kill him.
As to Thanos' chances, unprepped, against Prime - he's got none. Prime is generally way beyond anyone on the DCU earth and he's certainly beyond anyone on the MU earth, Thanos has no defence or power that could remotely slow Superboy from getting his hands round his neck.