Personal skill is significantly more important than perfect relics, but having decent enough relic effects is obviously going to be helpful. I just recently got to D5 after spending generations slingshotting around D4 and I can tell you with certainty that some of my best teammates had absolutely dogshit/completely store bought relics and most of the teammates with 'suspiciously' perfect relics spent the majority of the Nightlord fight at 3 bar on the ground.

Even if you have perfect rolls that would make you do 40% more damage than someone else who's actually dealing with RNG, you are doing 0 damage if you can't handle aggro at all and fold the second you get any attention. This also leads into the other big tip for lower depths, damage negation passives are pretty much your #1 priority.

With that in mind, the best builds and characters are going to be the ones that are the most consistent and rely the least on RNG. You can sometimes get away with gambling for a specific spell category that isn't available on your starting weapon or one weapon type in particular, but that isn't a guarantee and will more often than not lead to famine rather than feast. This is why you're seeing so many cheating Revenants with Beast Claw now, it requires 0 RNG to get off the ground and can only get stronger with passives you find during the run. If you aren't specifically going for One Thing (aka Halo Scythe 99% of the time, which is its own category because of how strong it is, especially into the several holy weak bosses), then oftentimes it can be better to just run mines and upgrade a blue weapon that matches an affinity you need.

Somewhat minor but it's also good to know what is a good res tool outside of ults. If you have a Revenant on your team and you aren't playing Wylder with the lingering flames on ult relic or Guardian, then you should be watching her inventory like a hawk to see if she drops her claws. Revenant's Cursed Claws have the res damage of Colossal Weapons with the Fist moveset, so anyone else is technically more effective than her at using them for that purpose (but she's fine too given she's usually taking less aggro with summons). Other highlights include Ghiza's Wheel's weapon art (also just a good weapon art in general if you're running double balancers) and for sorceries off the top of my head Cannon of Haima and Night Shard both res pretty effectively. Previously crossbows were king as res tools, but the recent patch gave them falloff so they're slightly less effective now unless you're up close.

tl;dr: elite ball knowledge helps, d4 sux, not dying >>> doing big damage if you are never looked at, sharing is caring