Bill Zebub
“It’s probably Matt Mercer’s fault.”
The ultimate point of a RPG's mechanics is to introduce surprises - stuff that people aren't just going to agree is what happens next. I mean, if the mechanics didn't do this then we could just proceed by way of agreement and free-ranging negotiation.
What elements of the fiction are within the scope of such surprises is a matter of rules design. Just to give one example, in 3E, 4e and 5e D&D a PC is basically always able to move wherever they want, subject to rules about unoccupied squares and the like. This is not a site, in the fiction, of surprise. Rather, these rules facilitate other stuff - like the making of attack rolls, the forcing of saving throws, etc - which are the site of surprise.
But in Burning Wheel - just to pick an example - movement in the context of the extended melee conflict rules (Fight!) does require an opposed check against one's foe. There is a possibility of surprise in a site of the fiction that does not yield such possibilities in the last 25 year's worth of D&D.
Or consider spellcasting: again, in D&D a player's declaration that their PC casts a spell is typically always successful - spells are not miscast and don't fizzle, etc, except in very particular circumstances. But other RPGs are quite different - Rolemaster is one; Torchbearer 2e is another.
And the same variety of possibilities and approaches obtains in the context of social elements of the fiction. In your approach, the PC is only affected, socially, if the player chooses to play their PC that way. So in the context of the process of play, it is all about the player making decisions for their PC, and others going along because they respect the players' "ownership" of their PC.
But in a game with social mechanics, how a PC responds socially can be a matter of surprise, just as (say) whether or not an enemy hoplite runs the PC through with their spear.
I agree about the necessity of surprise, but it is not sufficient. The card game War has a surprise with every turn, but because there are no decisions to make (and, more specifically, partially but not completely informed decisions) it's boring for anybody over the age of 10. Participants must have more than one choice, and the optimal choice must be unknown, for the 'surprise' to be meaningful.
Elsewhere I've criticized for the TOR 1e Journey mechanics for not allowing any decisions. There are multiple dice rolls, by both GM and player, with plenty of surprises, and some nice flavor text. But no meaningful decisions.