Depends on how much sheet AD you’ve got and the density of the enemies.
The maximum density you’re likely to see on a regular basis is around 30 targets within a 10 yard radius. You can get this with some good mob types, like Horror/Mother or Lacuni Thrall. A few others, like Swarms or any time there are Maggot Brood around, can exceed this mark and probably get up to around 40 targets within 10 yards.
So, let’s look at 5, 10, 20, 30, and 40 targets. With 1 target, the effect of AD is obviously zero.
Let’s assume you’ve got the max (useful) amount of AD: 178%.
And, let’s assume your “base” damage to each target is 100.
With 5 targets, you are hitting each for 100 damage directly, and they then take an average of 100 * 0.2 * 1.78 * 4 = 142.4 damage. So 242.4 total damage, and 58.7% of your damage coming from AD.
With 10 targets, you are hitting each for 100 damage directly, and they then take an average of 100 * 0.2 * 1.78 * 9 = 320.4 damage. So 420.4 total damage, and 76.2% of your damage coming from AD.
With 20 targets, you are hitting each for 100 damage directly, and they then take an average of 100 * 0.2 * 1.78 * 19 = 676.4 damage. So 776.4 total damage, and 87.1% of your damage coming from AD.
With 30 targets, you are hitting each for 100 damage directly, and they then take an average of 100 * 0.2 * 1.78 * 29 = 1032.4 damage. So 1132.4 total damage, and 91.2% of your damage coming from AD.
And, with 40 targets, you are hitting each for 100 damage directly, and they then take an average of 100 * 0.2 * 1.78 * 39 = 1388.4 damage. So 1488.4 total damage, and 93.3% of your damage coming from AD.
So, the effect of AD is obviously pretty enormous. It doesn’t quite reach 99% in this example, even at insane levels of density, but you are not far off of 90% with just 20 targets, which is easy to find, especially if you are helping things along with Spear and Stomp.
On the other hand, what Free actually said is that “99% of your damage comes from those hard-casts on Physical cycles”.
If you imagine that you are basically hard-casting during 100% of your Physical cycle, and just spinning regularly the rest of the time, then your damage profile looks like:
Seconds 1 - 12: 1x damage * 12 seconds (@ 100 “base” damage), so “1200” damage total.
Then, Seconds 13-16 (Physical cycle), hard-casting with varying amounts of density…
5 enemies: 3x * 2.4x * 4 seconds, so 2880 damage, 4080 total (over all 16 seconds), 70.6% of damage during Physical cycle.
10 enemies: 3x * 4.2x * 4 seconds, so 5040 damage, 6240 total, 80.8% of damage during Physical cycle.
20 enemies: 3x * 7.8x * 4 seconds, so 9360 damage, 10560 total, 88.6% of damage during Physical cycle.
30 enemies: 3x * 11.3x * 4 seconds, so 13560 damage, 14760 total, 91.9% of damage during Physical cycle.
40 enemies: 3x * 14.9x * 4 seconds, so 17880 damage, 19080 total, 93.7% of damage during Physical cycle.
In reality, I think most good players are going to be hard-casting more frequently than just during their Physical cycle, which means the “hard-casts on Physical cycles” damage share is going to be a little lower than the figures here.
But, the basic point still stands: the lion’s share of your damage is going to come from the combination of AD + CoE.
Definitely not taboo to mention, but any guide that doesn’t mention AD or hard-casting in this build has some serious problems! As for why that is, I have no idea. The process over at IV is not really transparent. Here on the forum, we spend a ton of time talking shop, trying things out, testing, analyzing, etc. IV may just have one guy kind of phoning it in without getting into any sort of in-depth thought, testing, or analysis. I don’t know the folks over there, I’m not sure if anybody else around here does, either. Some streamers are like this, too (though others, like Wudijo, are among the most overall knowledgeable players around).
Bottom line: keep a critical mind when it comes to advice from any source- and that includes regulars here like me or Free or Chris. We’re all human, and screw things up from time to time.