All i know that DD is going to lose next arc and luffy is going to move onto big mom
but crocodile and moria are still getting stronger and relevent in the story its silly to think DD would be any different so in that sense he might really be a yonko by the end, people still have to replace the people luffy will inevitably take down, plus theres the possiblity of shanks being taken down as well, and since luffy wont care about that and it would be silly if all the supernovas became new yonko DD is a prime canidate.
i see DD and crocodile as really similar, they are both the first real tests for luffy entering into the grandline/new world and as such i think just like how crocodile got a real wake up call from luffy so will DD.
plus DD is more then just personality, hes connected to so many other characters that his presence in the series is just as high as people like shanks.
he was introduced during jaya, he is a huge part of laws history and potentially kids history, he was a big part of shabondy and the war, hes basiclly been a major figure in a lot of the arcs so him just becoming irrelevant is stupid, but that does not get away from the fact that big mom is stronger and that DD will come before big mom.