Most wise players do take it into consideration, when I look at the latest Alcast information I note what conditions he does it under and that his trials groups will have much better uptime on buffs than mine.

In theory though an organised trials group should be build around these expectations and people should be organised into bringing or doing what's required.
Everyone should be working on expectations of what their groups can achieve not on perfect situations. If you have bad uptime on resource skills from your team, have people bring a bit more self sustain until it improves with practice etc.

Most Builds are optimized for vTrials where these conditions are the norm

I put Elemental Drain on my Templar when I heal, but then again it's pretty pointless to do so when both your DPS are Stamina.

There is an easy fix for this. DO. NOT. PUG.

If you want optimized set ups you need to realize that you are not just optimizing yourself, you are optimizing as a group. Sure you can do the best you can solo but it won't be as good as if you do the best you can as a group.

You forgot the 3rd assumption: You are in a raid guild with organized groups.

I have been attempting to run ele drain on my healers since "that's what good healers do"

at the moment characters that got anywhere near the kind of content that will genuinely benefit from it are templar and the sorc.

having elemental drain on my sorc means sacrificing something else, since I have to dedicate 2 ability slots to matriarch and that usually ends up being elemental blockade. because I tend not to run with perfect and min maxed groups my ability to guarantee 100% uptame for elemental drain is .. not good. it doesn't help that I have yet to find a reliable way of tracking it other then watching for that tiny rotating flame animation around my target - which is also a crapshoot. oh and lastly my chances of running with 2 magicka dps are also a crapshoot.

having elemental drain on my templar surprisingly also means that I have to sacrifice some other useful utility ability, and to be honest, I have found radiant aura to be a much better option for minor magicka steal not to mention its benefit and ease of use for ME, assuming my tank is taunting, so debuff portion of the elemental drain is covered.

now I'm sure in an organized group, especially trials group where everyone is minmaxed to perfectly synergize with each other - elemental drain is far more useful. in my experience. I'm about to end this silly experiment and just use something that I personaly in my particular situations find more useful.

I slot it if I notice my healer doesn't have it.

I have a few flex slots, but typically I am losing something else to slot it.. Resistances, Sheilds or have use spell power pots (which are expensive) rather sloting a skill to get major sorcery.

I never rely on tanks having ebon, 17K hp or die.

I don't expect pugs to. With friends or a vet trial group, I most certainly do.

If I (the healer) am not supplying ele drain, then either magicka is DEAD and everyone is stamina builds, or I fell asleep at the keyboard.

You can always expect to have a trial setup exactly the way you want it to if its an organized guild run.

I do

I slot ele drain on my healer, some bosses and groups I can keep it up 100% of the time.

But if you put me with a bad pug group on the final boss of falkreath hold, I'll be spending so much time keeping everyone alive I won't have a second to hit the boss with ele or lay down an elemental blockade.