I feel every class is as they should be for the most part. Some tweaking needs to be done but the only OP class is getting a nerf next patch. Scoundrel/Operative. They are backstabbing for 8k if they are any good. Highest hit i have heard was almost 10k. Marauders are exactly how they should be. As a commando it really is the only class that gives me a hard time, but I make them work for it. They have to pop their leap, vanish, and possibly their defense if they dont want me to kill them. But they make me work for it as well. You need to kite them as a ranged character or fake them out so they cant interrupt you. Also the DoT spec can be cured if you have one so there are ways around it all but they are as strong as they should be. That being said, with any class if you had the same rating of gear, they aren't going to stomp your face in. Stop comparing what either a lvl 50 does to you as a lowbie, or take into account they have better gear or you dont know how to counter them since you have not learned how their class works.
Also, your main goal against any class is learn what that class does. For instance, try to get a marauder to use his leap on you and or vanish early in the fight BUT dont cap their resolve. Example. I have the pushback on my melee stocktrike attack. Use it while strafing and try to create distance to make them use leap. If they use leap then you are free to use Concussion charge and create a large gap again. Any good marader will need to vanish at this point. It can be hard to hit them with Stealth scan or an aoe as they will be moving faster and even so they will be on top of you again. Next all you have as a trooper is cryo grenade, but then they have a cc breaker if it hasn't already been used. At this point if it all happened fast they will have max resolve. Usually a good marauder will kill me but that is what they go through to get me. Space everything out if you can and counter their gap closers. Easier said than done but it can be done.