You need a definition of a role. Attributes, ability scores, abilities, etc... are the definition in D&D. When the OP talked about not being "forced" by the game, he was talking about a role restricting him.
You can have definitions of a role that have no mechanics. However, unless the role has boundaries and characteristics (which should be limiting or else they are not really boundaries or characteristics), it is not a role.Well, we do have definitions for what they mean, in the RAW, that tell us how we are intended to use them. There is some shift in the mechanics of how they are to be used through the editions, but the fundamental concept is simple and goes all the way back to the introduction of these 6 attributes (although wisdom, intelligence and charisma have all been refined through time more than the physical stats have been).
If I play a character with a high intelligence, he should be able to achieve things that require a high intelligence. If I play a character with low intelligence, they should not be able to achieve those same things. When role playing the low intelligence character, we should be doing our best to imagine and pretend that we're in those shoes.
And even if a role playing game does not provide any rules or mechanics for intelligence - when we define the character, it is something that has relevance and will likely need to be addressed when something challenges the intelligence of the character. If we decide they're just as smart as us - fine. However, even with no mechanics for it, someone might decide that their character is not the sharpest tool in the shed and not use their full capability solve problems that arise before their character. That is also a choice. Regardless, in D&D, we have mechanics for it - and they should be used, not ignored.