Heatgerk - Trust the system?

I have been getting quotes to replace my oil system. I'm most tempted by heatgeek which seems the right balance of thoroughness and price.

The main issue I'm having with accepting it now though is some of the choices the AI or whatever makes on which rads to replace and with what. My kitchen in particular is the biggest room in the house with the highest heat loss (>2k). The rad in there at the moment is significantly undersized and is only meeting about half of that at deltaT50.

It wants to replace it but only with a type 11 in the region of 1100-800 mm wide depending on what pump I go for. Google reckons that is going to give off somewhere in the region of a quarter of the heat demand at 50° FT (what I'm assuming it's working to based off the efficiency). There are no restrictions on the space it can use for a new rad.

The engineer said he's surprised by it but he's been told before to trust the recommendations as it's working on the house as a whole rather than individual rooms.

Anyone have any similar situations and how did it work out going with HGs recommendations?