As far as class balance goes, Warriors, Spellslingers, Espers are fine as is from what I've seen. If you are having issues with getting killed playing those classes, it's your bad. Medics are considered OP by some but at the very least they might end up being sleeper OP. Their damage starts off weak but they are a very complete package. Stalkers are fun and a fan favorite. They are bursty as hell and I imagine they would make really sick grinders.
When it comes to Engineers, a lot of engineers complain about the class. My theory on that is that maybe people are picking engineers to play a pet class, but then they realize later on that they aren't really a pet class so then they focus on the weaknesses. They are supposed to be a tanky ranged class. Their damage is probably the lowest of every class on average, but it's like that for a reason. I personally think they are fine. You might need to change your playstyle up or pick another class. I didnt even get to touch the warrior or engineer, but I've watched that one set of youtubes of the guy playing his engineer and I know first hand that warriors are fine. That streamer wasn't even playing the engineer well but he was managing. You might have issues later on dealing with white damage, but I never played them so I don't know what else to say.