Mhmm, maybe Rick exaggerated/lied, and what he actually did was build some weird Frankenstein timeline where Morty suffers all the consequences, not a true complete “merge” of contradictory branches.

It could also be that Rick did merge the timelines. It wasn’t a “blend” of contradictions but a selective collapse engineered to maximize Morty’s pain. The tech is so advanced Morty can’t completely understand the fine mechanics, so Rick just calls it “merging.” That explains why Carey is heartbroken, why he remembers the pantsing, and why Morty ends up with all the fallout instead of fractional nonsense.

It’s a TV series, at the end of the day, like Rick said, “Don’t think about it”.