It's not quite like that.
What they effectively did is separate the story from the class - you can play a particular story, but choose to play as a different class than was originally tied to that story. The only restriction is that you can't mix Tech and Force; so you can play the Trooper story as a Smuggler (and vice versa) but not as any of the Jedi. And, conversely, you can play the Jedi Consular story as a Jedi Knight (or the other way round) but you can't play any Jedi story as a non-Jedi. Same is true for the Imperial side of things, of course.
As for DPS performance, it really mostly matters if you're playing high-end group content. If your goal is Master Mode operations and you really want to optimize, there's decisions to be made depending on what you're most likely to be used for. But if all you're doing is the Story Mode solo content and maybe a group every now and then for weeklies or a couple of Veteran Mode flashpoints here and there, then you probably don't need to worry much about performance and can focus entirely on enjoyment.
I don't know the current state of the game that well (7.0 kinda killed it for me) but at least just before the expansion DPS performance was actually fairly well balanced. Differences mostly come up on very long or very short fights - a burst-heavy class/spec will do a lot better in solo content for example where things die in seconds; while a DoT-heavy class/spec will do better in operations when things live for many minutes. Same with AoE capability: more important in dungeons and solo, and for certain operations bosses.
Give that you can switch fairly freely now, there's many options to pick from. If DPS is your goal, having one burst spec and one DoT spec to switch between as needed would seem like a possibly good compromise. That way, you can play solo as a more bursty spec, and when you're going into a big-boss ops you can take the DoT spec instead.
Which ones you want to pick is largely preference at this point, I'd say. You can have a look at some parsing data at, say,
Parsely and compare. But the usual caveats apply: this is a very select kind of data collection subject to specific biases, and may not reflect your own preferences. But it gives a rough idea about relative spec performance - and also shows you that most are reasonably close to each other.
In terms of utility, I don't know how things have changed. Bounty Hunter/Trooper used to be very in-demand because they had stuff like grapple to position targets and some nice cooldowns; but I don't know if that's still as needed as it used to be. Most specs have some kind of utility that may be wanted depending on content.
For solo consideration, I've always liked having the option to use stealth - it makes heroic missions significantly faster to complete. If you don't do those a lot, it might not be that important for you, but for me personally I found it the biggest QoL improvement (but I'm a sucker for heroics).