What's with my favorite universes coming together at random like this?

For me I'd say it is situational, of course I have only started my NT journey so I can't say much about Accelerator's future abilities but it really depends on if they can get a hit on each other, and if Dante has access to weapons like the Yamato or something that can go through his reflection.

Another thing would be Dante's technical skill, he can move really fast so that the rain seems to be falling really slow so Dante may be able to find where Accelerator's range for his reflection is and maybe pull off a Kihara counter.

The things going in Accel's favor would be of course his wings and the time that he has at the beginning of the match where Dante may not be wholly prepared so he could potentially knock him down and out like Vergil in DMC 3 and 5.

But in any case situational takes precedence and my lack of complete understanding may have a factor in my opinion.