Overall I feel she had the worst cameo of the 3, if only because she really didn't do much upon her return and lost early in the tournament. She was basically treated poorly in order for the writers to glorify Iris and her Dragonite.
I was really talking more in the context of others reactions I've seen towards Dawn's return on TV Tropes(really, that place is getting more and more unreasonable and elitist. I'm on the verge of wanting to stop going there). I personally didn't see a big deal other that the surprise I mentioned at how she had more episodes(from what I've read and what little I've seen, the B/W anime is becoming more unpredictable than D/P was).
I knew Piplup was more popular in Japan, but that I didn't know that much at the expense of Dawn's character(she really is becoming a female Ash).