Sentry shares surface similarities to Superman, yes, in that they both held similar places in their respective universes and both have an S on their costumes and both are mighty, mighty types. Once you scratch even vaguely beneath the surface, that's where those similarities end.
Age of the Sentry is where this is lampshaded most seriously (and it is an amazing mini, anyone who has not read it needs to go read it seriously) but it's plainly obvious that once you get there, Sentry is more 'Miracle Man' than he is Supes, really.
When I, or even Enz, say he's 'Not Superman',. we're rejecting what is, to us I think, relatively shallow ways to characterize him, you know? It's not a refusal to acknowledge that there's similarities or debts or direct acknowledgement of tropes, but rather, that there's just more there beyond the surface than people want to acknowledge when they're busy dismissing him as 'just another clone'.
Blue Marvel and Hyperion are /way/ more indebted to Superman than Sentry is and are both far straighter takes on him.