If SE didn't intend for Cleric Stance to be used in instances then they have horrible playtesters - all they'd need to do was enter Sastasha as CNJ. We also had speedruns of WP that maximized healer DPS even when PLD's enmity generation was complete garbage (ty Cover). Small adjustments were made to healer DPS, but nothing that outright stopped you from doing it, and those adjustments were mainly AOE related such as the infamous Holy nerf(s). If SE did want to stop it, they had 2 years to do so. If it wasn't intended for 2.0 they were definitely okay with keeping it in.