Macato is an off field engine made for Harumasa, don't use it for Seed.
Chain attacks are rare, Seed Anomaly doesn't happen often.
Macato will spend a huge chunck of the time providing Seed +0% ATK.
When you occasionally cast EX, you will have 10% ATK for 8 seconds.

vs.
Cannon Rotor, is a proper on-field engine, will always give Seed a permanent +12% multiplying ATK ~= it's roughly a +350 ATK bonus.
Plus it's thematically fitting because Seed is heavy weapons expert.