Most 18W I know of are typically non-Master volume amps. You can always ADD master volumes to non-master volume amps. But if they get their distortion from the PI and power section like old Marshalls and Voxes, you still can’t put a useable loop in it.
Some companies actually do put useless loops in their amps knowing full well they are not very useful. But all the salesmen and literature can honestly say; “Yep, it has a loop.”