No.  That's always been the trick with non-Master Volume Marshalls, they have to be cranked to get that legendary sound and they are very load amps, often their output rating is very conservative.  You have to remember, you are meeting the 50-watt RMS rating at peak clean headorom, to distort those power tubes you are peaking well above that.  Imagine the 100-watt 1959x model.  Admittedly the '70's JMP's were a little more aggressive (and harsher) than the Plexi's Nik replicates, but this something you'll find with many amps around this size.