You're not wrong, and when the part being cut is worth 5 figures for the raw stock, it's probably a criticality, but it's important to not gatekeep this process, lest it become a no-true-scotsman kind of thing.

I built a couple of 3d printers from scratch BECAUSE the various components were cheap and approachable. Haven't done CNC because my interests haven't taken me there...but the thing about advancement is: While one fella is saying 'You can't do it that way!' someone comes around and does it that way, and the first person is left in the dust.

You can't really stop Laser printers from dropping to many thousands of dollars to $70...all you can do is ride the wave.

The probability of any given step being missed is proportional to the amount of value lost of the step is missed. Pretty weird how that works ;)

That's not necessarily true, it all depends on what your desired outcome is. Stepper systems can be open loop as long as you're aware of what the torque threshold is and make sure you don't exceed that. Obviously a crash would exceed that, but there's ways to detect that (e.g., stallguard on Trinamics stuff) without adding an encoder. The whole point of open-loop stepper systems is that you make sure you stay under the torque limit by a margin (say, 30% or so) and you are fine. A properly designed system should never lose steps ever, besides in a crash event. Or if you load it up with too much side force, but you can get that on any machine.

Servos and closed loop systems are almost mandatory on large commercial mills due to the sheer scale and mass involved, but they’re not as mandatory on the hobby level.

In practice, hobby level machines don’t have near enough rigidity or spindle power to warrant high movement forces in the first place.

Nearly all of the hobby CNC machines on the market use open-loop steppers. They’re definitely not losing steps during normal operation.

The topic of steppers vs servos has been covered over and over on every hobby CNC forum for the past two decades. Closed loop systems are great if someone has extra budget to spare, but they’re unnecessary for machines using hobby-level spindle power.