And so long as the heat pump and radiators are appropriately sized to dump heat into the house, that shouldn’t matter.
The main issue is people with badly designed heating systems running at 70 degrees flow temperature.
When you swap over to a heat pump, the flow temperature is only supposed to be 40.
So you either need to get more water in the loop (bigger radiators) or less heat leaving the building (better insulation). And an understanding that the heat pump is supposed to heat gradually.
As for the installation cowboys…yea, it’s an absolute farce. £2k unit somehow costing £20k to install.