For starters, Pii as Kuro is young spirit, they both act more like passive buff rather than conscious as Zeno is.
Secondly Cecil wasn't interacting with Bertia as much as he did in isekaied timeline, so there have to be little "brainwashing" as it took at least 4 years for prince to feel anything, he was emotionless android from the get go.
Since meddling of isekaied Bertia, Heronia had much higher difficulty in the real world, all the people were completely changed and so do events where she could interact with Cecil, which to be honest would be
very frustrating so kinda no wonder isekaied Heronia acted furious.
Imagine re-playing a favourite game you mastered and suddenly everything going haywire not according to the script, something even isekaied Bertia is surprised to feel.
I'm not sure this "what if" Pii has shown will effect current Cecil, think he will snap out of this eventually, only wish it wouldn't effect isekaied Heronia, it's actually not her conscious fault Pii acted that way...
Both isekaied Heronia and Bertia should finally meet, Cecil knows she said several times about game mechanics names same as Bertia did, he isn't that dumb to not make connections...
It's very sad that Pii committed suicide for Heronia happiness, not knowing that Cecil already is not careless mannequin, only if both villainess and heroine interacted before this...
Thanks for the scanlation!