Look back at the vast majority of Taker's career and there is a hell of a lot of dross in there, moreso than most guys would get away with. Could that be the character driven style holding him back? It could well be. I hate nothing more than watching old Taker matches, they always disappoint me.
I'm not saying that Taker isn't an above average worker, I'm saying this notion that he's one of the greats is just wrong.
I'd have him as one of the greats. Is he as good of a wrestler as Bret, Angle, HBK, Benoit? No but for someone his size, he's done quite well. Him and Bam Bam are two of the best big man workers in wrestling history. Maybe I'm missing another big worker in there but I can't see many better than him.
Undertaker was fed the likes of Giant Gonzalez, King Kong Bundy, Yokozuna - freaks who were limited in the ring, those matches apart from one of the Yoko matches were god awful, but who could do better? He was fed Khali, he was given freak after freak in the 90's.
If we look at his matches against Angle, Mankind, Austin, HBK even the Sid Vicious match at WM13 wasn't bad even if Sid shit himself. His matches against Kane were good, HHH feud even with the buried alive awful gimmick, he has worked in all sort of gimmick matches and has done a very good job with them. The gimmick is larger than his ability but I think you're discrediting him far too much.