It's hard to say. He got both LHW and HW titles, which is a huge accomplishment. Even while he never beat Jones to get the LHW belt, he beat all of the top LHW rivals and looked like a guy who was far and away the best LHW during that time, while Jones was suspended and whatnot. He's still undefeated at HW, he still won that belt and the Strikeforce HWGP. He's still arguably in the discussion of HW GOAT (I still favor Fedor, myself, but DC is certainly still a viable answer to that question).
I don't think it matters if he's the common answer to the HW GOAT question or not though. All said and done, he's absolutely one of the best MMA fighters we have ever seen, a class act, and will be remembered as such.
I don't think Jones would have moved up to challenge him if DC hadn't moved down. He's never given us any indication that he will ever move up to HW except flapped his gums about it for years. Would DC have lost to a guy like Ngannou? Maybe, maybe not. Fedor's streak is remarkable bc most HWs can't keep from getting KTFO at some point. Fedor was in trouble a few times and managed to win where others would have probably lost (Fujita fight, Randelplex). I suppose that if we go on pure skill, DC is a guy who possibly could have made it through years of close calls at HW. Even though Jones knocked him out, perhaps DC's chin is better at HW where he isn't draining himself to make weight? Lots of heavy hitters at HW too though, so who knows?
In all honesty, it is doubtful we will ever see a streak like Fedor's again at HW. But if we do, that man will be in the conversation of HW GOAT.