The "riddled with state machines" from the post I was replying to, while sounding negative, is at least better than the "single state machine" which is probably combinatorially huge and would be impossible to maintain.

My rough rule of thumb based on experience is that if the state machine being a state machine is visible outside of it's internal implementation (compared to just an interface with operational methods that don't hint at how things are managed behind the scenes) it's probably too leaky and/or incomplete.

I would trust code with extensive state-transition testing (regardless of internal implementation) - I wouldn't trust code that claimed to implement a state machine and didn't have that testing, or extensive documentation of edge cases and what was left out of the state machine.

As a simple example of something that's often left out in a way that fucks up state machines: the passing of time.