Why would you ever play ARC? I Hate the Class System.

[Sephrick]

Because they're redesigning the entire stats and combat system again and giving new abilities so we really have no idea what any of it will be.

[Malakhim]

If it makes it any easier for you, classes are essentially going to be strictly "freelancers" a la FFV, which can mix and match any of their learned abilities based on the situation, whether it be soloing or playing certain light party content where it's more effective if everyone can hold their own for example, whereas jobs are simply specializations or "load outs" out of a squad-based FPS or something that will limit your scope of available actions, but make you much more effective in a given role for those moments when your party requires a much more organized layout and extra oomph for a full party raid or something.

Obviously if you're going to be stuck on one type of content, then you probably won't see the utility of whichever, but that doesn't mean it isn't there. Personally, I see class variety becoming VERY useful in PvP if done properly.

[Yrusama]

If it makes it any easier for you, classes are essentially going to be strictly "freelancers" a la FFV...

I never thought of it this way, but you're absolutely right! Amazing observation! Can you be my new friend? :3 FFV is an underrated game.

@OP: It's good to give feedback, but there is a point where you would be telling the devs to completely rework the system and delete entire items (I'm rather proud of the Obelisk +1 I made and don't intend to get a relic anytime soon). There are some benefits, like the class gear, to playing classes over jobs.
You gave THM as an example, which is able to use AoE Sanguine Rite almost instantly for party damage reduction and MP regain. The most THM loses from BLM are Convert, Sleepga, Freeze, and Flare, which are all situational spells (a THM can use Chameleon). Burst is highly overrated, only acting as a faster and cheaper Thundaga. Any THM can pretty easily rival BLM in a straight shootout.