I mean is that all you can say, like duh.
The Cal Tech paper, 1997, appears to be somewhat ground breaking in Industry at that time. Therefore the FETS used did require an large drive 10 watts. Pg today is many time less, than ten w. Note the authors state, the high internal temperatures were caused by HIGH drive, ten watt, requirements. Pg = po/pin log 10 = 13 db
The internal structure of the transistors used were NOT designed for high speed switching.
The choice of water cooling was chosen for some reason, not immediately clear, but they state power eff at about 90 percent.
Therefore if YOU disregard drive, 10 watts (quite high), no amp today would require this, the power the water takes out is 20 joules/second or in engineering Parley 20 watts. Water cooling for twenty watts seems an over KILL, but this paper is 20 years OLD. Its interesting this is like a Marconi paper, since Cal Tech would like to believe they were cutting edge.
They suggest such designs may be useable for ham operators. Probably .. but the ground breaking design did have some heat issues to resolve. Also , that ten watts of drive should be added into the twenty watts the E amp cost in switching. So, you're looking at 30 watts of heat. Also Yips, that supply Vdss seems real high. You could hurt yourself!