"Her mom works at the same place."
And boom goes the dynamite!
"It’s not that hard to sell $4000 of food (ie you turn 15-20 tables at $40-$50 per diner and serve 80-100 total ie any busy but not insane shift) during a weekend dinner shift at a busy Olive Garden or Outback, and it’s genuinely easy if you work anywhere that involves most people ordering 2+ drinks of alcohol."
Your numbers are about 2x reality. And the tip rate at places like that is closer 18%. And most importantly, someone without experience isn't getting the prime hours like your friend did.
I'm not dispelling the notion that young people can make good money as waiters. Just saying that it's not like it's some easy path that anyone can quickly jump into.