GobHag
Adventurer
It is, but also because there's an extra step between non and Darkvision, low light. And one extra step beyond that called Greater Darkness which can only be seen through with greater darkvision.I recall PF2e being even more permissive with light: Darkvision has no distance limit, works on magical darkness, and has no dim light radius, it's just all bright.
I'd argue that it isn't self-defeating at all, like I said, It's meant and treated like just another aspect that might hinder a character like difficult terrain, is it 'self-defeating' when a level 1 character can have fire resistance(and remember that PF2's resistance is numerical and not a flat halving) so they can walk past a line of hot coal without taking any damage and at high-level might be able to just completely resist the fire damage from a bonfire? Does that mean fire should just be removed from the game?
Double Slice sidesteps the penalty from successive attacks, does that mean the penalty from successive attacks shouldn't exist? Of course not, there's opportunity cost for taking darkvision at the low level, it's not a big cost but it is a cost. And chugging darkvision elixir at level 3 will take a dent to the party's economy.