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

[Quesse]

requires partying for any decent method of gaining experience (pre-50) or tomes (post-50) if no one is playing the content.

I just leveled WAR/BLM/PLD to finally get my crown. Did it all via FATES/farming/leves - mainly because I was trying to get my Choco to Rank 10. I play very off and on and tend to spend a lot of time crafting, messing with my house, and other stuff. It didn't seem to take too long. I'm just not sure if by 'decent method' you mean 2-3 days or if a couple of weeks. Then again I played FFXI so 3 weeks to go from 1-50 seems like an instant.

In any case I would disagree with "not playable" and "waste of time" assessment -- it just doesn't match your more hurried style of play.