Agreed.
Without knowing the comparative resistances, it's foolish to draw any definite conclusions about power levels.
Either Gasly was running comparative DF and had a more powerful engine, in which case I don't understand why he didn't win the GP. Or, Gasly had less DF (which is why he was slower around the lap) in which case he would be able to outdrag Hamilton even if he had less power. Personally, I suspect the latter is the case.