Bendis did say Void was lying during the entire Dark Avengers run. That includes the sun showing often cited as proof of how Sentry gets damaged because he wants to.
Again, proof from interviews is silly and we abide by comics. Void lied when he said stuff like he was Galactus or that he could restablish what Molecule Man warped if he wanted to.
Sure, which is something I believe too. But he also said in that same statement that we shouldn't trust Void and that he obviously meant to leave things ambiguous because of the nature of the character. He was clear about the battle on Siege itself, but the implications concerning Void's powerset were on the open.
Captain America damaged him with such buff, how much higher than an Herald level can Steve become when boosted with the Norn Stones? Again, I do think heralds did damage him and Thor proved as much when he killed him. Did Sentry make it easier? Sure. Can he beat most heralds before they ever got to the point of killing him? I say it's likely as long as we take the battle in Siege on face value. But I thing people are allowed to argue depending on different powersets without it being facetious, considering how Sentry/Void were written under bendis, that's all.
There is definitively an issue with how obscure the showings were, it's understandable to have a diverging opinion on the character. With such room for interpretation we don't need to agree on everything, most of the Sentry fans I've argued with have been rather laid back and respectful.