For the most part, this has very little to do with how much power the amp has, and more to do with what type of pot was used for the master volume. I hear this a lot on TB where people talk about the amp being SO loud "because I was rattling the walls with the volume on 3." More than likely, it's not the power section, it's the fact that they are using a linear pot for the master volume.
If you use a linear pot, the volume will increase dramatically in the first portion of the pots rotation, and less dramatically as the volume knob goes higher. A log (logarithmic) taper pot is just the opposite and will give you very little output in the the first half of the pot's rotation and an increasing amount as the volume knob get's closer to max. A log taper pot is supposed to more closely resemble how our ears perceive volume. It's a common practice for amps to use a linear pot to make it seem like the amp has tons of power. From your description, it sounds like your amp uses a log taper pot. It might only be putting out 10% to 20% of the amps potential volume with the master volume up 50%. What's important is the actual output volume of the amp and not the position of the volume knob.
To add:
My Eden WT-500 came with a C-taper pot, which is reverse or anti-logarithmic. This makes for an even greater surge of volume in the first 1/3 of rotation than a linear volume control. I suspect that the rest of the WT-series are fitted similarly. I've since changed to a normal logarithmic taper, though I think that linear might be a good compromise, as I'm finding the volume increase a little slow until 1/2 rotation.
