No, not using a rule for this at all. Here are my items:
Group Thermostat “Thermostat” [ “Thermostat”, “Fahrenheit” ]
Number:Temperature Temperature “Temperature” (Thermostat) [ “CurrentTemperature” ]
Number:Temperature TargetTemp “Target Temperature” (Thermostat) [ “homekit:TargetTemperature” ]
Number HeatingMode “Heating Mode” (Thermostat) [ “homekit:TargetHeatingCoolingMode” ]
I simply say “alexa set temperature to 70” and after the thermostat and openhab are freshly started I can go over and literally see that the temperature set on the thermostat has changed. But if some hours later I try adjusting the temperature again the item changes in openhab like before but the thermostat itself no longer changes.