If the cable running out of the panel to the heat pump does not have a neutral (just 3 wires, hot, hot, gnd,) then, yes the loads should always be balanced (unless there’s a fault.) If it’s got a 4th wire connecting to the neutral bus bar, then it’s possible that it wouldn’t always be balanced, but not sure if there would be any case a heat pump would be balanced when heating and not when cooling.
