I totally understand the concerns you guys bring up, I play a dps operative for my guild, but this issue really isn't that bad. You have to make your group aware your class has a huge burst dps opening if you can start from stealth. The way we do this is I stand stealth in the back of the room well out of the range of the bosses ability to see through stealth which is about 30m from what I've noticed. Our tank then engages the boss first and then I run in, I am still stealthed and out of combat at this point where I can run safely behind the boss and start my dps rotation.
Also if you see that big target on you while you're stealthed you have about 5 seconds to pop out of stealth and nothing will aggro as long as you break stealth. The key is getting a good hang on the range each boss can see you from and staying out of that range until the tank pulls or you start the encounter.
I have completed all the raid content in the game with my guild so far and have had no issues starting on any of the bosses from stealth, including fights like the infernal council or ancient pylons in the eternity vault. So it can be done, you just can't be in position before the fight starts, this does two things though, allows the tank to establish aggro and for you to pop your relics at the start and get a huge burst damage at the start of a fight which makes up for the time lost running up to the boss.
I understand that there are workarounds as i use them myself, but I do not think it is intended or necessary for stealth classes to have to tiptoe around the content like this.