That's a theory I've been thinking of.
You may think "that's be a cop out" but no, nothing done with the Caitlin we know at all hints at her going down a Dark Past.
If someone had watched Season 1 of Smallville genuinely ignorant of the Superman mythos, that Lex Luther had at the potential to turn to the dark-side was still obvious.
Same with the Star Wars Prequels, even if you showed to someone who legitimately know nothing about the OT, the foreshadowing on Anakin's dark future was still there.
And even using a non Prequel example Faith in Season 3 of Buffy, she was set up as the Dark Slayer form the start. But she didn't turn evil till the season was like 2 thirds over.
Caitlin Snow is a much more obscure figure, people who are ignorant of her being a villain in the comics are not so rare. To any of them the Caitlin we've been following suddenly turning evil would seem like an ass pull.
I don't have any particular reactions to the latest episode. It was good.