I wonder if that was an intentional tonal disconnect?I'm not trying to change your mind, just responding to the ideas here:
In most respects I feel that Honor Among Thieves was more serious and less Guardians-like than I expected. There was definitely some verbal humor but a lot of the gonzo stuff I saw in the trailers turned out to be from backstory/exposition rather than from the mainline plot, which was played pretty straight.
Mainly though I want to comment on the magic level. There was kind of a weird disjunct where the protagonists have an expectation of high magic and casually talk of wizards, resurrections, "knowing a druid," etc., and yet regular people still stare in wide-eyed amazement at a cat turning into a human. It seemed inconsistent and a bit too... protagonist-centric(?) for my tastes.
I've had many, many DMs who try to play the, ordinary town with ordinary people yet the PCs suddenly experience high levels of magic completely inconsistent with that.
Or maybe it was a much simpler explanation, the background actors were told to act like they experienced wondrous magic and overdid it for the effects later added.
I enjoyed the movie but tonally I found that odd in the same way I found the casual horse thievery odd and somewhat alarming.
I laughed at that, because, again, WAY too many groups where casual thievery (horse and otherwise) was basically the norm.