Piplup and Lucario were definitely the most promoted Sinnoh pokemon...but of all time? I'm not sure. I think the Kanto starters, Mewtwo, Jigglypuff, are still more well known.Piplup & Lucario are among the most popular Pokémon of all time so their placement in the movie didn’t seem weird to me at all.er.
I honestly think the only reason Dawn's Piplup was so promoted is because originally they might have planned to evolve it like May's Torchic, but then changed their minds when they saw how marketable it could be as a Piplup. It might also have to be that they wanted May to grow more visibly stronger with her starter evolving, whereas Dawn always had more of a performer aspect in her battle style so they had no reason to evolve it.
Although it's weird as hell to think of DP pokemon as "10 years old" now given it's from 2006/2007. I honestly remember when DP was the recent gen just airing, hard to believe that was a decade ago now.