I don't know where you got the idea that Pierrot copies Mappa. Pierrot is older in the market and has more influence. Not that I defend the studio, their behavior is bullshit when it comes to filler. They're fanboys and bad guys fucking up by stuffing a lot of crap junk chapters into good stories and making mangakas flee for overwork, but copying is the first time I've read it.

One thing Pierrot is respected for is the wit and originality of his stories. Besides, being one of the oldest studios in Japan. Mappa for them was an anomaly, they even had to create a specialized area for adult content. Hence the new Bleach raw adaptation. :P