Yeah, that is in fact generally how its used.
"We ate the rest of the cake" means the entire remainder of the cake
"Sarah got a trophy and the rest of us got nothing" meaning everyone but Sarah did not get a trophy.
" We split the rest of what was leftover" meaning we split everything that was remaining
So yes, "the rest" is used to describe the entire remainder of something besides what was highlighted. In your case you highlighted his Ult and the entire remainder would, in fact, include his Q. I'm no sure why you wouldn't just point out that you didn't want to include his Q in that instead of argue over semantics when you're wrong about that anyway as well. Maybe try being more specific instead of vaguely asking for an ult nerf and buffs the the rest of his kit. We as readers have no idea what you're thinking and the way you worded it you for sure included his Q.