Why, would that make Wlad more of a champion than he already is? Paper titles mean nothing. Fighters make the belt, the belt doesn't make the fighter.
If Wlad holds all the belts he is UNDISPUTED until someone beats him. As long as there is another belt - especially one like the WBC ie highly regarded prestigeous title there will always be someone that can say "oh but that other champion...." hold all the belts and you are IT. There is no other champion.
Its not even about belts. If it were you would have the claim the WBU, WFF and a dozen other paper titles. Wlad could drop all the belts and he would still be the heavyweight champion of the world.
It is assumed that Stiverne and Arreola will fight for the title. I believe that Arreola will knock Stiverne out and become the first Mexican world heavyweight champion. Wilder would get knocked out by almost anyone.........
Based on what Arreola would beat Stiverne? Stiverne beat him clearly the 1st time, dropped him hard and broke his nose. Only Arreola's chin helped him to survive 12 rounds.
If the fight is between Arreola and Stiverne, i'd go with Stiverne, even tough Arreola can surely do better this time. But there are other contenders better than those two, namely Haye, Tyson Fury, Kubrat Pulev and Povetkin.