You can't really say "shaman combat rez is useless because DPS shamans are discouraged from using it." In some situations, you want to save the combat rez for the tanks or healers because in most situations, losing one of those means you lose the fight.

But I can think of plenty of situations where you're not in danger of losing the tanks or healers, and instead you're butting up against an enrage timer (Maloriak is a good example). Losing a DPS shaman's contribution is going to trigger the enrage, and you lose. If the raid leader isn't capable of recognizing when DPS is more necessary than ensuring that a tank can get back up, that raid leader needs to re-evaluate the mechanics of the fight. Are the tanks properly mitigating damage spikes? Are the healers overtaxed because of fight-specific mechanics?

And it goes both ways: did the DPS shaman die because he didn't have situational awareness? Was it just RNG?

Combat rez is an important tool, but you can't give the tool to more classes without limiting it. Otherwise you have encounter designers putting instant-kill mechanics back into encounters, because that over-emphasizes the importance of those classes in encounters. It violates "Bring the Player." The shaman's self-rez is a valuable that shouldn't be dismissed because it's not automatically useful 100% of the time.