I think wires are getting crossed here on the "useful" or intrinsic value of land versus the market value. The GP was arguing that the land value is separate from outside considerations like amenities.

People argue this over things like gold as well. IMO at the end of the day its impossible to tease apart anything other than the total market value, and I think that's where you are at as well sticking to the land's total market value.

But presumably at least some of the land owners are already paying more through paying for the presumably private amenities. Hence the fairness argument falls at least partially.

Taxation is not about fairness, it's about raising revenue for the rather discretionary spending of the government.