Less to do with the calliope and more to do with:
- Stuart rush + M5 quad combo is powerful as hell
- Double m1919 on riflemen are way too cost efficient(especially when they hit vet 3)
- Recon run is amazingly powerful
- Strafe can wipe support teams or lone squads if they stay in the targeted area
If the only thing good about this commander was the calliope, I'd treat it like I treat the pershing commander. But all these things together just makes it way too strong and meta that even nerfing the calliope wouldn't put it out of flavor.
It's kind of like they took shock frontline and made an equivalent for USF.