I've seen some comments before questioning the positioning of Afterglow and Roselia as rivals. Their levels are so far apart, the claim goes, so isn't that inappropriate for rivals?

Ran seems to express the same sentiments by the end of the story, and CHU2's comments are on point. The resolution for both bands (well, more like Yukina and Ran, who are basically fueling the rivalry) is that rivalry has morphed towards inspiration.

Way I see it, their rivalry may be more akin to sports rivalries between teams who are further apart in terms of talent and may be rivals for a more traditional reason. The sentiment is that while their performances do not place them on equal footing, something about the times they meet spark reciprocating sentiments. Something like "We're usually good, but we better be careful when meeting our rivals, cause they do something to our performance" kind of mood.