I’d actually be surprised if those Phoenix blocks are much better than MT60s. With a screw terminal you have a mechanical connection that can work loose (especially in a high vibration environment), and not all conductors are necessarily in good contact. Whereas solder (especially good old Lead solder!) tends to form a much more solid bond.
Also, in most use cases (i.e. at anything less than maximum speed and torque simultaneously) there is more current flowing through the motor wires than the power supply wires, due to re-circulation at less than 100% PWM duty. I can get away with a 10A fuse on the power input, despite driving my motor at 50A, for example.
That said, I wouldn’t advise to skimp on the power supply wire gauge, because you don’t want excessive voltage ripple putting noise into your system or straining the DC bus capacitors. This doesn’t apply to the motors, so your motor connector and wiring are only thermally limited.
The gold plated brass pins and sockets on the MT60 connectors are about the same width as 10AWG wire, and the wire itself acts as a heatsink.
I wouldn’t imagine you’d need anything much heavier than the motor winding tails themselves.
If you want to go full-on industrial, then use a crimped connector like Anderson Powerpole.
Another thing to note: In enclosed spaces and under prolonged usage, the ODrive itself will NOT handle 100A continuously on one axis, never mind two. The PCB itself is nowhere near as heavy gauge as 10AWG wire, never mind 6 or 4, and the FETs start to get hot around 80A. You will need forced air cooling.