Regardless of levelling or max level queues, nothing's going to change because levelling through dungeons as a tank/healer isn't efficient anymore due to a few reasons:

1. FATEs and levequests are just much better for exp.
2. Chance of getting low/bad DPS players because it's Duty Finder.
3. More tanks/healers prefer to run with people they know (FC mates/Friends/Linkshells) than to gamble on the chance of point no.2