Until someone figures out how +elemental damage factors into elemental reactions (and I still think, especially due to most people maining claymore users anyway, it's not worth it) it's likely still +ATK% > Crit Chance > EMastery

You'd get a lot more value out of flat damage on low damage characters like the archers. I doubt Claymore users get more out of flat attack in substats than crit (especially since substats only boost, randomly, every 4 artifact levels after 8, so a flat attack substat is going to start low and in terms of probabilities, likely stay low).

Crit in this game at least acts pretty normally, so you want to tune it at the rate of 10x(crit chance) = crit damage

That is to say, since crit damage STARTS at 150 in this game, you want 15% crit chance before they become equivalent, and then for every 10 CHD you want 1% CHC. Each point in either is reduced in power once they break that 1:10 equilibrium ratio.