DND_Reborn
The High Aldwin
I remember back in 2E once we actually broke down abilities into 3 "components", each ranging from 1-6, so the total of your components was your ability score. An example would be Ug INT 6 might be acuity 2, recall 1, reasoning 3. FWIW, 3-4 was "average" for a component. Such a PC might be able to solve a puzzle (reasoning 3), but as you suggest have horrible recall and weak acuity.I see the disconnect lying with how the stat is distributed against these three pillars. INT 6 means "acuity 6, recall 6, reasoning 6". Sure you can envision a character raised in the woods and for some reason having nothing to recall at all and no need to recall anything in his education, so he never trained to it. I'd say it's OK, but it would be "acuity 10, recall 2, reasoning 10" to make it 6ish INT. I'd probably want this character to be INT 10 and take a flaw of a -4 penatly to knowledge skills as part of a custom background (balanced by other things). Other would say that the -2 to knowledge skill (the mechanical parts) are enough to reflect the three pillars of intelligence, and if you're not going to roll the other ones they can be roleplayed freely. Different takes, I guess, as others would want all three aspects of the INT stat given equal importance, whether through rolling a skill or roleplay (and a third group wanting to roll everything anyway, including player-solved puzzles).
But since 5E doesn't break things down this much, a INT 6 IMO would overall be "weak" and if the player puts such a low score in INT, the PC should be played to reflect that score. I am NOT saying the PC needs to be played like a complete idiot or anything, but the "role-playing" should be embraced by the player to make the character outstanding. Weaknesses can be strengths in other ways.