Why Ingenuity I and not Ingenuity II ?

[StouterTaru]

Ing 1 + 2 Standard Synth = 20 Durability

Ing 2 + 3 Careful Synth = 30 durability

That's the main difference.

BUT, those two standard syntheses require steady hands to remain up, the three careful syntheses do not. Depending on your rotation, this could mean a 3rd steady hands for an extra 22 CP, or not.

Ing I + 2 x Standard Synthesis = 24 + (2 x 15) = 54CP

Ing II + 3 x Careful Syntheses II = 32 +0 = 32CP

The math above doesn't work; when you have enough craftsmanship to finish with Ingenuity I and 2 Standard Synthesis, you're well past the point where you need Ingenuity II to finish with 3 Careful Synthesis. Those might have been swapped, and the poster meant Ingenuity II and 2 standard synthesis (62 CP + possibly an extra 22 CP) vs Ingenuity I and 3 careful synthesis (24 CP). That leaves 38/60 CP for 10 durability, which depends on your rotation.