Are all those abilities you mentioned standard or does he gain them as the game progresses? I'm not talking the durability, I'll give you that one because he's half demon. I mean the briefcase, stopping time & summoning a shadow clone. I ask because I honestly don't know. They sound like abilities/items he would get as the game progresses.
If he doesn't have them the entire time I don't see how they would factor into a completely random fight where he would have no time to go and gather these items and abilities. With his standard sword & pistols there is no way Dante would have the firepower needed to even KO Wesker.
Weaker however would already injected himself with the Prototype Virus and have his super speed, stamina, endurance as well as his own God like durability.
Dante is the son of Sparda and is no slouch. I have no doubt he would give Wesker a run for his money. A half demon wielding a sword and a pair of pistols isn't enough to defeat a self styled God.
Something else I would like to point out. Dante is half demon and that's the side that gives him his immense power and durability. His other half is human meaning he can still die. It would take a long time to accomplish but Wesker is one of the few left in this tournament that can do it.
Wesker still wins this in what would be an amazing battle that destroys the Danger Room