Is there any way to play the game as DPS? Or just end subscription?

[Risvertasashi]

Try finding a Tank or Healer who's about to log off for awhile to queue you into one of those low level dungeons you need to level up, and then they can just leave when the instance starts, and a Tank/Healer queued in progress can replace them. If one doesn't show up, you can just leave without a penalty and try again.

I'm just kidding this would be a very selfish approach.

If you use this method, make sure you're set to 'English' queues only. Otherwise you could be waiting for a replacement for a very long time.