The dice- or rules-heaviness of a game is something that theoretically can be adjusted. Practically, that may be more or less work depending on how integrated versus modular the design is. Probably most significant are the expectations of players, and that "gamer culture" is shaped in turn by how the game is presented. It's partly a matter of selection: People inclined to place great importance on "official rules" and "carefully engineered balance" are less likely to dig the tenor of (e.g.)
Tunnels & Trolls in the first place.
General ethos can be conveyed even before getting down to mechanical details. There's an
Exalted book with an "homage" to the first cover of the 1e PHB, that in style presents a very striking contrast.
... in a dice-lite game, a painful introvert cannot play the party's face man.
Unless someone's too introverted to play an RPG in the first place, that should not be a problem. I am pretty introverted, and more to the point a bit clumsy (by "hard wiring") in the social interaction department -- very far from ever being a salesman (or for that matter an actor on stage and screen)!
Despite that, I am a fan of bringing role-playing into such encounters. The key is that it's the
substance of the overture that matters, not the artfulness of one's thespian delivery.
What I've found in recent dice-heavy games is that the concept of "role playing" has shifted away from approaching problems from the character's perspective (as the player's number-crunching replaces that) and toward the sort of "acting" that entails accents and mannerisms. That may create in some minds misleading assumptions as to how things must work in a game in which role-playing is actually an integral (indeed the essential) part of play.
That brings us back to how expectations shape the way mechanisms are used, and how design and presentation are more or less compatible with different approaches.
When social skill ratings, combat powers and other factors are wrapped up in a "zero-sum" sub-game, especially one that in various ways (including sheer volume of rules and assumed investment of time and energy) is elevated to great psychological importance, then people tend pretty naturally to oppose weakening the influence of those factors.
It is in my experience easier to "house rule" a game from rules-light to rules-heavy than vice-versa. Something like 3e is one possible end-point if one starts adding chrome to Original D&D, something like 4e another. Empire of the Petal Throne, Metamorphosis Alpha, Chivalry & Sorcery, Villains & Vigilantes, Starships & Spacemen, Arduin, RuneQuest, Advanced D&D, Gamma World, RoleMaster, Palladium ... a host of games arose from such tinkering. The more complex the offspring, the trickier it is to "repurpose" them.
My default "go-to" game is the systematic but extremely modular Basic Role Playing foundation underlying Chaosium's RPGs (most famously
Call of Cthulhu). I find it a bit awkward for vastly superhuman characters -- D&D might work for a scenario involving the likes of the Crimson Bat, but I can't see doing that in RQ -- just as games designed with comic-book heroes especially in mind tend to be less satisfactory to me when applied to grittier, "street-level" topics.