As you said, running continously is the ideal point for heat pumps. And for a continous load most radiators are big enough. In Germany they were scaled so they could heat up the rooms pretty quickly and then idle for time. Since thats not the goal with a heatpump we can use the idle time to even out the lower peak capabilities. You loose the ability to quickly adapt the room temperture, but with outdoor temperature probes connected to the heatpump this istn an issue. I am in the process of retrofitting my home to a heatpump and that what the engineer told me at least.
A bigger issue seems to be the single-pipe heating vs. two-pipe heating systems, but those are not the majority in germany and should be phased out anyway because they are so inefficient.