It is though. Oda didn't want zoro to have supreme blade yet hence in both cases ryuma and oden were not given one and both mog lujitorra.
With Oden that's not the case, there's no plot, Oda could just make one of Oden's blades a Saijo or not give Zoro Enma at all, he could give him Nidai or something else.
If some "random" character gets a Saijo I'll admit I was wrong but so far only the strongest in the verse hold one and Oden isn't among them.