Ok, so there is an option for Global Bypass of Cab / IR / Neural Capture (but only if the Capture Type is set to the ‘Cab’ category? If so that seems odd as there are so many captures of amps out there, that will be assigned to the ‘Amp’ category, so it would be a lengthy process having to go through them all to change them to ‘Cab’)
However there is no Global Bypass for Amp blocks? Is that correct? Doesn’t really help with using the QC for 4CM if there’s no global bypass for amps.
If I am building a preset that is intended to be used with an emulated amp, or alternatively with 4 cable method, I always build in some method to switch between the loop block and the amp. When the loop is engaged to switch to 4 cable method, the emulated amp is bypassed. When the amp is on, the loop is bypassed. The switching can be achieved with a stomp button, or with scenes.
Good idea 
I’ve never really understood why you’d use 4CM when you have so many amps on tap in a unit like the QC but I’ve just got my first tube amp (yes, all these years playing and I’ve never owned a tube amp) which is a Laney Super Cub 12. It sounds absolutely fantastic so I’m actually using the QC with it just for fx for now, so the 4CM is something I’ll be experimenting with now
You can use QC for effects only and (assuming the Laney has an effects loop) still utilise the 4 cable method. For instance, you can use the drive type pedals in the QC, loop out to the input of the Laney, back out from the Laney’s Send into the QC Return, then add modulation and delays and reverbs, then output into the Laney’s Return and power amp. It keeps delays and reverbs a lot cleaner than going through an overdriven preamp. You also have the option of using the Laney pre-amp or an emulated amp using the switching method I mentioned above.