I regularly tell people how to do mechanics in mentor roulette and I've never been banned or warned for it. As long as you're not being rude like "omg this stuff is so easy you guys suck, you just go to x spot", you're not going to get in trouble. Instead of saying "this strat is bad" you can pretty easily just offer an alternate way of doing it if you're worried about getting in trouble. I think people overexaggerate how easy it actually is to get in trouble in this game. I saw someone on my server angrily link a google doc of his ex girlfriend's nudes in shout chat, get reported by a ton of people, and the guy was still standing in Limsa every day after. So yeah, you probably aren't going to get in trouble for offering some advice on a fight if you aren't bringing up stuff like parses.