I think you've nailed it there. There's a bit of a hangover from hating Txiki/Ferran too because they're seen as the guys who got rid of Mancini to bring their own guy in. Pellegrini was dubbed a yes man and a stopgap and now they don't really like Pep for the same reasons.
I'd add the contempt he appears to have the for the derby.
Pep treats it as just any other game and that is hard for some fans to comprehend as it used to be the only thing we had. Liverpool, Chelsea any team that dares to challenge us he takes seriously, an Ole managed United can get in the bin with Palace, Wolves etc.