Maybe don't dance around the question regarding your suggestion then. You still haven't explained the economics of your suggestion to use GSHP as the next step a house builder should make instead of investing in other areas of the building first (having lambasted ASHP as a half effort). Money isn't a infinite resource and, as such given house prices are already extremely expensive, to push further burden on buyers has to be justified. Therefore its more effective to pick the lowest hanging fruit first such as an ASHP and ensuring the building itself is as efficient as possible (thus reducing your overall heating demand and negating the need for expensive to install and slightly more efficient heat generation).
If you can't make the connection between an air con exchanger sat next to a house vs a heat pump exchanger then i can't really help you, go use google to see what they do. There exists billions of these units all around the world and somehow having one in the garden of a UK home is now a quality of life detriment as you put it. Its a little bit ludicrous. You'll find (as with most aspects of change) its not the existence of the machine thats the issue, its the communication and expectations that have not been set correctly. If a home builder decides to put a double unit in front of a window then thats on them for lazy placement/plot design.
Even if you gutted a building every 40 years for refitting that would typically not include insulation in external walls or the fundamental construction of the building where this initial investment by the homebuilder would be made. Neither is there a great need to insulate internal walls (which home builders have largely been removing anyway in order to sell more homes with less space). GSHP increased efficiency becomes largely irrelevant when you start building close to passive house insulation standards. The point being here the money is better spent avoiding the problem which is heat loss than spending to get slightly more efficient heat gain. Sure if you want to build a house where its going to -20 all the time then go for GSHP, it'll probably make economic sense. In the UK though that largely isn't the case.
Furthermore, you seem to be making things up, I have never said it was my view to do the minimum. You're the one expecting companies that exist to make profit to make irrational decisions regarding their costs and what’s effective (over the base regs which most will be adhering to for profit reasons), for then the buyers to accept that and pay more, in a market where buyers are already quite financially stretched. I'm the one asking you why you think a company like this should be so inclined to spend money on a GSHP before better insulation, given that regs do not require them to actually do either.
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