are side quests really just meant for one class?

[ruskie]

the game is so DPS bias. Healers can't possibly kill as fast as other classes

Sorry what? Maybe astro is a tad underpowered(though if you get lucky with the cards that becomes a non issue really) in the DPS department but both SCH and WHM can pump out some good DPS. WHM burst while SCH sustain DPS. I've never had a problem or feeling that I'm killing something slow on any job other than paladin.

[Nutz]

Honestly side quest exp is not much better than daily clan hunt exp (roughly 25k per mob group -- totaling 375k exp or so). These can be done surprisingly early if you have a good chocobo and don't try to rush it. By 52 you should be able to kill anything. Of course that won't get you very far by itself, but the point is that side quests won't either. Do them when you feel like it.