I main tank. But switch to healer and DPS when they are in need.
Often in DR raid for dps.
Outside expert I saw dps or healer in all other queues at least once last week.
I think if tanks are the issue then give better rewards for tanking.
Ie job in need points to be spent on mog station
every job in need check where the job in need does not change it stacks up to 10 points
1 point = 1 cent.