9 monsters within 10 yards of the source is 10 monsters in the area. If you say a pack of 9 monsters, than a max of 8 get hit by the explosion.

The Focus part would make AD very competitive but, not always better. For example on a weapon you have to choose between 10% damage or 24% area damage...as we saw above if it was working right and you had a pack of 6 then 24% AD is the equivalent of 24% damage, so weapons is a massive win for AD. In fact, for 24% AD to give a 10% damage boost you only need 3 mobs next to you (.24x2x.2=9.6%). On rings 20% versus 50% crit damage is dependent on your CHC and existing CHD, and in a Broken Promises build that's not an easy number to obtain. Assuming 50% Crit rate and +250% crit damage as a base then you bump your damage for :

Non Crit = 100, Crit = 350, Average hit = 225

After bonus CHD Crit = 400, After crit ring average hit = 250, Increase of 25/225 or 11.1%.

Higher crit rates make CHD a bigger upgrade, lower existing CHD also makes it a better upgrade. Compare to 20% AD which (if fixed) provides an 8% damage boost at 3 mobs, 12% at 4 mobs, and so on from there. There's an argument to be had there too. But AD is always just a damage stat. CDR is often a survival tool on top of being a damage increase. The +0-40% damage from 20% AD compared to +20% damage from CRD plus getting to 100% uptime on a defensive cooldown is a very tough tradeoff to make.

The end judgement is that if it worked as promised, it would be a very interesting stat. When you see the GR 74 clears with literally 15 monsters constantly being pulled in by the support monk you start to wonder if AD is one of the best stats. But then you think about Rift Guardians and leaping hit hit the mobs on the edges and Seven Sided Strike taking you half a screen away and out of the pile...consistency is worth a lot. MAybe next season we can try it out.