I understand the use of cleric stance in solo content. Fine.

Now if cleric stance is disabled in PvE dungeons/raids (like in PvP), the issue of people complaining you are not dpsing enough will dissipate, possibly.

Yes you can still dps, but just not as much.

Right now, I feel like in cleric stance, I can dps more than the casual dps, which means I am fulfilling two roles, healer AND dps. Which is not the intention, I believe.

So should SE disable cleric stance in party instances?

This is only in the standpoint of game design, and not numbers, or completing instances faster etc.