Cable sizing is very interesting, I just went through this on an EV project at work.
You have to balance voltage drop, heat generated in the wire, constant current, peak current, and size and weight of the cable.
That being said 2awg should be more than fine. It has a continuous amp rating of more than 200 amps. I?ve used 8awg for rear mounted battery setups without issue. Peak currents aren?t that high high with a starter. You can run them through a 150amp fuse/breaker.
The issue comes when you have poor crimps and corrosion, or the starter spins the motor over too slow (usually a combination of corrosion in the wires and all the connections).
What Patrick is dealing with is a starter that won?t actually spin anything when hot. It has nothing to do with the cables, and everything to do with the starter and most likely the solenoid.