That is true. But I think the reason of it in DxD case is that Naruto is a likeable protagonist, while Issei... not so much, I guess. Sure, he evolves, but it is quite subtle and in the start he is not a charismatic person.
It is a similar case with Familiar of Zero, people dislike Saito so most stories change him, most of the time by putting someone else in his place. Louise is not liked much either, but they see her as a bit sympathetic since the start with being a failure, so her future behavior is a bit also caused by Saito being an enabler (I know, rune brainwash, but this justification only appears a long time later and until then people saw it as him being like that just because).
Now, most DxD crossovers suffer one problem I think is a big plot hole...
By the end of the story, Naruto basically became a bodhisattva, or at least Kishimoto really wants to point on this direction. Now, and this is canon, Evil Pieces do not work on buddhas, even mutated pieces. Since from what I could find a bodhisattva already acquired buddhahood (actual therm I found) but decided to stay in the world for the benefit of others (buddhists feel free to correct me)...