It's not a tube vs transistor issue. I've had numerous amps all rated for 100W both tube and SS. Some sounded like kilowatts, some sounded like milliwatts. Some were just not a good match for certain speakers. Just trade-offs in the design/price. I could be more specific with the individual models but that would serve little purpose and be misconstrued as criticism.
"tube watts" versus "solid state watts"
I'm sure you, like me, have seen it written more than once that brand X tube amplifier, rated at 30WPC, sounded more powerful / more authoritative than brand Y solid state amplifier, also rated at 30WPC. Or that brand Z tube amp, only rated at 15W, was comfortably able to drive brand A speakers, because those 15 were tube watts and therefore up to the job. Heck, I think I've even heard the phenomenon with my own ears.
My question is: is there any basis in electrical engineering for this effect? Can we say scientifically what's going on here?
My question is: is there any basis in electrical engineering for this effect? Can we say scientifically what's going on here?