A 500 km3 landslide moving 100 m/s will have an energy of 1.125e+19 joules and could produce a tsunami with 5.6225e+17 joules or over 134 megatons of TNT which is around 20 times the energy of the Tohuku Tsunami. Hunga Tonga’s eruption doesn’t represent the peak of eruption intensity and as such its tsunami is not the pinnacle of tsunamis of that kind. There is a firm cap on how much water a volcanic explosion can interact with but it’s a safe assumption in my opinion that a truly intense eruption could produce a tsunami with 2 or 3 times the energy of the HTHH tsunami.