Honestly the easiest fix to this is to just make more fights put out more damage. When you can spend anywhere from 40-70% uptime DPSing without the tank or anyone slipping below 50% health, of course DPs is going to be prioritized. If only because you get bored and are just sitting there twiddling your thumbs.

If people want healing to be a priority, rather than make complicated systems they just need to encourage the dev's to make more mechanics that hit harder.