Not sure I totally agree with this, though. I agree that the thespian/acting/portayal portion of the game shouldn't be elevated in importance over the more mechanical portions as a general rule.
But I think the core of an RPG, as opposed to something like a board game, is the conversation shaped around creating a shared fictional space. That conversation is then guided by the system and rules (and social contract), and the boundaries it imposes on how that conversation is shaped.
Skill checks, resources, combat, other forms of resolution method; all of those, at a zoomed-out level, exist to let the rules shape the flow of conversation and the declarations of what happens next in the fiction.