Base load air-water heat pump for 30% living area?

To me, that sounds like a heating engineer who doesn't believe in individual room controllers, buffer tanks, and bypass valves and just explains everything in a somewhat complicated way. You could even expect a properly designed underfloor heating system with low supply temperatures (not 35°C/28°C) and reasonable heating circuit lengths. I would probe him further, but he would definitely be shortlisted if it all turns out to be true.

An air-water heat pump requires a minimum flow rate to be able to defrost in the event of icing. It is important that the underfloor heating is designed for this.

Renouncing individual room control is desirable but does not help with this.

For a single-family house, a small temperature difference is typically necessary here so that the volume flow increases. However, high volume flows mean higher pressure losses, ergo smaller circuits.

Additionally, the heat pump must not be oversized.

For this reason, many companies install a buffer tank so that they do not have to design the underfloor heating carefully. However, this is absolute nonsense and only costs money.

In the end, everything must be properly balanced hydraulically and thermally.