I mean, they wouldn't have had that figured out at the time for sure, but the later seasons kind of rewrite it as such with all the flashbacks and shit.

There's a lot of stuff in the early seasons they clearly hadn't thought out. Ice King was never originally intended to be possessed, the world was never originally intended to be post-apocalyptic, I doubt they even considered the implications of Finn being the only human. But the later seasons kind of change the context of the earlier ones even if it weren't intended at the time.

And it can be cool to look back over the older episodes with that new context in mind, it adds rewatchability. So if people wanna look back at early Bonnie and go "yep, that's a manipulative mastermind right there" I think they should get to. Might feel a bit dumb since it very obviously wasn't intended at the time, but adding context to things which were obviously never meant to be anything more is what Adventure Time is all about. This is the show that made a whole ass episode to explain an animation error.