point one: no, i believe you are mistaken. glacus is not basing the idea that narrative language should be mechanically weighty; "immersion" or inhabiting a mindset or otherwise roleplaying is usually a fiat thing. and fiat is the furthest thing from concrete; interacting with emotions, beliefs, and motivations in a concrete way will require mechanics - narrative in nature - that make these things matter.
point two: sure, i'm saying that as a gm, that these players do exist, because i play with them. and that one day you might have to deal with their desires, and they may not intersect with yours (the horror!). which leads me to the last point.
point three: of course the gm is also a player. of course they should also have fun at the table. but when someone wants something different, you're going to have to deal with it. you must decide whose enjoyment is going to win out. and you can save yourself a lot of grief by preparing for it.