Yeah, 50000ooo... guy gets it, KHORNEY maybe listen to him a bit. I build
on several supports, but on others I know I need a
.
Those arnt the issue, I build
on Zil too, need the slot efficiency.
I tend towards something more like:
and in that last slot I build whatever is needed for adaptation.
Some good items that can always help the team:

All of those have different reasons to be played by a support, and help your team over helping you.
Ever built a frozen mallet and permaslowed an enemy champ while speeding up your team? Thats support, and that frozen mallet slow is the same weather I have 100 or 500 AP, and in the right situation, my team is happy I have it.
Enemy team has no good split pushers? Build a Zz'Rot and force them lot lose a tower eventualy or for them to break off someone to deal with it.
Frozen heart, enemy team has a Yi, Xin, Trist comp? Frozen Heart saves your team a ton of damage with the ATK speed slow.
Enemy team has 4 AP champs? Time for the Iron Solari. Your team has 4 AP champs? Time for the Abys. Scepter.
They all have ways to help your team, and they require you to see the advantage you can create for your team with them.
Sometimes a single item with the intent to support your team can be worth twice the damage you could deal in a team fight.
Lastly, yeah, sometimes that last item is a
because we need more damage to close out the teamfights in our favor, but not every match needs a deathcap.