My first/best example for how loosely Larian handles CR, and monsters in general, is the first possible battle after the crash. An intellect devourer is a CR7(!) creature, with 71 hit points and boat load of innate psionic abilities, that should shred a full 1st level party in one round, yet we can easy dispatch 3 of them without getting hit once, by employing a bit of stealth and high ground advantage... if that's the level of adherence to D&D rules we can expect for this game, than they could have stuck to der Divinity system. I mean, sure, you can always say those are new born creatures, a lesser variant or they are weakened from the crash... but what I smell here is distinct air of:
"Damn the rules, it's cool so we do it!" followed by a slight breeze of: "...only because we market something as the sequel to a beloved gaming series, doesn't mean we can't do whatever we want with it."
Dont know where you are getting your info from but an intellect devourer is most defenitly NOT a CR7 challenge. A quick google search gave me this:
https://forgottenrealms.fandom.com/wiki/Intellect_devourerWhich shows a CR of 2. And the monster isent using its abilites. Which can be explained by the presence of the tadpols. Maybe they are just trying to disable us rather then kill us to prevent us from getting away.