That’s true, but the statement made to the OP is suggesting to “blast the heat, because the thermostat will run the engine hotter”. That’s the opposite of taking the heater core out of the circuit. My understanding is that whoever told the OP this believes that turning the heat on HIGH will somehow cause the T-stat to somehow run the engine hotter.
We might be overthinking the problem because of that strange statement made to the OP. Perhaps the best approach would be to revert back to the good suggestions previously made and step away from that strange statement. It might have been misquoted anyway. I know I occasionally misquote something told to me, and perhaps the OP did too.