on supports with either shields or heals or both i always get 
for the heal bonus that it provides to healing and shield spells(morgana, janna, orianna, lulu, lux, (etc) shields can heal with athene's. quite significantly if there are enough charges on it; i call it a "crit heal"). as far as i've noticed, hardly anyone else does this. am i missing something?
No, you're not missing anything, it's a very nice item for supports with heals/shields and the only reason it's not built that much is because people in low elo would rather build full ap on enchanters and "carry" because they don't find healing enjoyable. Really, it's a good item but underrated.
I hardly ever see any of the champs you mentioned. Not a support main but I think that enchanters are simply more effeftive as a cc/buff spammer rather than heal/shielder
I take it on Janna very rarely, but that is because I get more mileage out of her by focusing more on positional awareness, smart warding, disruption, and poke. The shield is a nice bonus but doesn't tend to win games on its own. As for Lux, I almost always buy this on her when I play support, and my decision to do so has only been proven since they buffed her shield. Morgana, I tend to try for tankier items on in order to ensure that my ult will go off in team fights and that I don't get blown up quickly, but this is a personal preference. As for the others, I don't play them very often so I cannot say, but I would imagine Lulu makes terrific use of as well.
Back when I did play SR and support, that usually was my first item on Nami, with Athene's, Ardent and Aery on her, a single E could potentially give them a Heal from Athenes (that isn't her main heal), movement speed boost from her passive, a slow from her E, a shield from Aery and an attack speed boost from Ardent. All that from 1 E.
Plus if you build other Forbidden Idol items without Athene's you are just wasting bonus Mana regen, when you could get Athene's and turn it into AP. Get it in ARAM too if I'm going more support Nami but more fun to go full AP in that most times.
> for the idiots who think they are far superior to their peers and their 10-6-3 games as a support that are losses are 100% their teammates fault.
It is how it is supposed to work, with charging it and using it for heal. 
together can be powerful even on non-enchanter like 
.
