To do the most damage, you don’t want to use Avalanche at all, as it lacks significant multipliers to do decent damage. Instead, you want to get all your damage from Earthquake, which means wearing the Girdle of Giants belt.
For more info, you can look at the Maxroll guide that DM linked, or consult my own guide on the build, which is the most in-depth source available: [Guide] MOTE6 Earthquake
Definitely not trash. WOTB - Insanity increases your damage by 50%, and like I said, you can essentially imagine Avalanche doing 0% damage.
The issues with Avalanche are several… first, its base damage (2400%) is much lower than Earthquake, particularly the Molten Fury rune (6000%). The 6600% you mention is with the AV:Volcano rune, but that amount actually gets split up between multiple targets, meaning that if there are 10 nearby targets, each only takes 660% damage, whereas with 10 nearby targets hit by an EQ, they’ll all take 6000%.
Second, it’s hard to actually apply AV very often. We can apply a lot of EQs because we cause them via Leaping, but with AV, we have to use shouts and hard-casting, plus Ground Stomp, if we are wearing Dread Iron. But even if we are wearing Dread Iron, we still can’t make as many Avalanches as we can Earthquakes.
Finally, we get a better multiplier from Girdle of Giants than we do from Dread Iron. DI’s bonus is additive, meaning it gets lumped in with stuff like TS: Falter, Brawler, Strongarm Bracers, etc. GoG’s multiplier is, well, a multiplier- a separate 3.5x buff-, not to mention, it’s bigger (+250%, rather than +200%). And, of course, we can’t equip both GoG and DI without losing Lut Socks, which would cut your EQ damage to 1/3 because you wouldn’t apply it as often.
When you compound all of this- the lower weapon damage of AV, the slower rate of casting, the weaker multipliers, and the fact that you have to nerf your damage in order to take Dread Iron, the final conclusion is just that it’s best to forget about Avalanche and load all your damage into EQ.
Demonstrating that fact is, well, every good clear with Leapquake recorded in the last few years!
Not even! At least WW does a lot of other stuff, even if it doesn’t do damage: it moves you around, generates your Fury, heals you, stacks Stricken. And, of course, applies the Rends that do your damage in speeds and vs single-targets. Avalanche literally doesn’t do anything… they could delete the skill from the game and hardly anybody would notice.