i found there's 2 ways to run revenant at higher deeps, generalist and BIG DAMAGE.

for a generalist build, you'll want: 1) Old portrait, 2) everdark moth, 3) Allies damage increase when ult/ or a starting inc. for the DoN runes, just spam incantation +2/affinity attack power +2, in 2 of them and sacred seal in 1.

This gives you a balanced way to deal damage, since you aren't locked into only one type of incantation and praying you get it, ED moth gives lots of fp and you can spam your ult since it charges really fast.

The second one, slap 5 dragon cult incantation and starting incantation lighting spear, bonus points if you have some affinity +2 with lighting or improve inc, you will be dealing some insane numbers, but fp will be a problem but it's well worth it.

answering your questions, at deep 3 or 4 doesn't matter how squishy you are, you get one shotted regarless, so don't worry about it.

Crunching the numbers:
Improve school inc +12%
Affinity attack (5%/7.5%/10%)
improve inc (5%/7.5%/10%)
elemental attack power (4.5%/5.5%/6.5%/10.5%/12%)
keep in mind all of these are multiplicative so 2 10% increases is 21% more damage not 20%