You are reducing it to a binary set of choices; either Disney leaves it alone or makes Pixar Pier. Your reasoning is sound in this vacuum, critiquing simply fandom reaction to these choices. But in doing so you are ignoring the infinite possibilities of what else could have been done, and even the execution of and quality of Pixar Pier itself. It isn't like they built a brand new land with high quality finishes, attractions built from the ground up, interesting dark rides, simulators, and a finding nemo sub ride.
They tacked on static figures to a roller coaster, built a really underwhelming googie / midcentury plaza, and named food stands after characters. I adore the new finishes on the pixar promenade and as you enter the land by ariel's grotto but the microbrew theme pulls you right out of the period-centric architecture, rendering the entire experience post-modern rather than properly themed.