So I did some DPR calculations comparing:
18-20/x2 weapon (e.g. Falchion, Scimitar, Fauchard)
vs
20/x4 weapon (i.e. Scythe)
Using a damage value of 100, and using crit chance calculated with the Flawless Belt + Keen, and taking into account +2 crit multiplier from Lethal Accuracy & Mythic Imp Crit:
18-20/x2: 100 -> 400, +300 damage, 300 x 40% = 120
20/x4 weapon: 100 -> 600, +500 damage, 500 x 20% = 100
so the 18-20/x2 weapons win in terms of average damage, which is expected, but it's mighty close.
But here's the thing: Fortune hex exists, and so does Brilliant Inspiration, and
so does Perfect Strike, which my build happens to have.
When you calculate using triple advantage, e.g. Fortune + Perfect Strike, you get critical chances of 48.8% for 20/x4 weapon, and 79.4% for 18-20/x2.
With these percentages, 20/x4 actually outdamages 18-20/x2 on average.
18-20/x2: 100 -> 400, +300 damage, 300 x 79% = 237
20/x4 weapon: 100 -> 600, +500 damage, 500 x 49% = 245
But you didn't think it would end there, did you? Check this out, I tested Perfect Strike, Brilliant Inspiration and Fortune hex all together:
Yeah, that's right. I'm rolling FIVE DICE and taking the highest. Of course PS only lasts for one hit, and BI decays once you get a 20. But still. This is nuts. Don't ask me how this works - I'm getting an extra die from somewhere.
This means, for situations where you are really stacking the dice and trying your best to get that crit off, e.g. on a boss, 20/x4 is actually better than 18-20/x2 for damage. Like, potentially
way better.
Of course there are other considerations such as Outflank procs. And some bosses are immune to crits. And also having Reach is probably still the most effective way to increase your damage. But still. This is nuts.