Its up to u
I remember when the game 1st came out, the average healer in parties weren't expected to dps
Hell lol remember failing the ultima story fight cuz the aoe dance was kind of hard?

But as the game progressed so did ppl's expectations of random healers doing their job and a little bit extra.
Technically ppl expect u to work harder and do both to make everyone's else life easier.
Only time i think u should consider in dpsing is if ur trying to help dps meet the check. Other than that just heal because dps probably won't help heal as to how u can help dps. ( the puny cross class cures and phys rarely help )