Same settings on each amp is potentially meaningless. The gain curve on each pot may be very different. Mesa amps have a reputation for going from zero to loud as hell when the master knob goes from zero to one. in comparison, the TecAmp has a much smoother taper on the gain/master. You would have to set both amps to full volume to compare the difference.
Also, the inherent voicing, as others mentioned, has something to do with it too. If the Puma has more of a dip in the mids, naturally, then it will feel like it is quieter than a more mid voiced amp. Similarly, the EQ knob settings will play a role in output volume. Noon on one amp isn't necessarily noon on another. The earlier generations of Puma have a bigger natural low end too, which eats watts to generate. That said, I have a feeling my M6 would be louder than my Puma if I raced them side by side, and it is 600 watts.
Which brings up a good point about watts and volume. You need to double the watts to get a 3db increase, which may be tough to notice at high enough volumes. So a 600w amp vs a 900w amp may be 300w difference, but it won't be as loud a jump as going from a 300w to a 600w amp. if you are running an 8ohm cab the 600 and 900 ratings at 4 ohms get cut to 300w and 450w respectively (roughly, though TecAmp claims a higher 8 ohm rating on their website).
Lastly, watts isn't just about output, but also about clean headroom. The MB amps have been noted (by KJung and others) as having more mid-range distortion than the Puma. It was part of the reason I went TecAmp over MB when looking for an amp to pair with my fEARful.
As long as it gets loud enoug to work for you, it is loud enough
