The Anima grind is not the problem.

[Aethaeryn]

So Heavensfire is roughly equivalent of 5 dex better and Armageddon has +4 dex. So in the absolute most extreme scenario, Heavensfire provides 1 dex equivalent more.

For reference, you can see the NIN stat weights above. SMN Stat weights are more simialr to 0.145 high for CRIT and 0.115 low for SPS

Are you disagreeing with me then? Can't really tell. Even if machinist's skill speed was closer in weight to dragoon or monk, Armageddon would only pull ahead by about 2 dex (assuming your crit weight example, which is likely close). That's less than difference between some races. Anyone who would find value in that difference at such a high price and grind point would probably already have the superior Gordian Musketoon anyway. I'm not touching it for now unless someone actually comes up with some real stat weights for machinist and shows that it's worth the difference.