If you put up essence of retribution does it just shorten the length of defensive communes like sanctuary, protection, divine insight etc. - or does it reduce their effectiveness as well?

Can you tell me, specifically, what "defensive" supps it nerfs and how it nerfs them?

Pro: noticeably increases damage sups like wrath, fire and brimstone, light if heaven, etc

Con: the hp you get from heal communes is cut in half, you might do cure sups at a lower level. I don't recall it affecting sanc timer but if it does it's only by a tick or two

Usual cavaet: I'm not a coder, but I've had the virtue, and did a little testing overnight.

Laxman pretty much covers it. Heal is only 50hp, and as best I can tell, looks like your protective/healing spells are communed at a lower level. On the bright side, sanc/protection are 50%/25% damage redux no matter what level, so that's just shortening the sup length some.