DD is not in the top 5 conversation because he has 4-7 losing matches and few if any 7-3 or 8-2 match ups. He simply does not have the match up chart to be top 5 if you believe the opinions of some of the best players using/fighting him.
I don't if those are the same opinions who think Bane 7-3's him. Nobody even comes close to bodying Doomsday (maybe Frost but I don't think that ever got fleshed out) whereas Lex, Bane and Grundy all get mopped the fuck up in some matchups on top of the ones that they arguably also lose, just not as horribly.
FK has Batman "losing" a ton of matchups too and not winning any by a large margin but he's still very much in the conversation.
The most relevant Bane when it comes to majors as of late has him losing to Flash, Zatanna, Sinestro, Batman, Shazam, Superman, Zod and maybe Batgirl but you'll argue he's very possibly top 5. Please show me a Doomsday chart with 7-8 losing matchups, two of which are quite possibly 3-7's or worse.
Nobody ever agrees on charts or tier placements and that's fine, but at least I'm almost guaranteed to see Doomsday in a top 3 whereas I have to pray to the fucking FG gods that my other mains will make one. I don't think the claim that DD is top 10-5 is so outlandish, especially by anyone so willing to put Bane there too.