You're being overly dramatic for a non-issue, especially on Elemental. I've not once had a Frontline match where there were 4 or more healers. Sometimes there's 3, but the majority of the time you'll have a couple of people do that awkward job switch dance until it's just 2 healers.

Adding job restrictions will only destroy Frontlines. Even if there was a restriction on the queue, people could just switch when inside. If you want to have control over your setup: roll a premade.