<snip>(1) what is faster.. throwing a main inside the panel... <snip>
I don't know about you guys, but by using both hands I can easily shut off a 42 space panel's breakers in under 5 seconds. So I don't see why a "main" breaker in a subpanel is worth the extra expense or fuss.
IF we were discussing a subpanel located a long way from the feeder's breaker and IF that panel is likely to need to be opened for maintenance or changes frequently, I could see that a "main" breaker in that panel could be a good idea, but it's still not required by Code.
Oh, and from some of the discussions I've seen on here, even having such a breaker does NOT relieve the need for PPE as even though the bus would be dead, the lugs aren't.
Tempest in a teacup...
Yeh, and while you were at it, Bob, you should have e-stops on every piece of equipment in the building.
Now that's funny.
Or how about a shunt-trip main?