Yes, the least productive 10% of land represents a much smaller percentage of food production. This is often land in areas that are most environmentally sensitive.

In the UK we pay farmers to raise lamb on marginal land yet they still aren't competitive with lamb shipped from the other side of the world. I'm not sure why we should be subsidising that, especially when there is a lot of environmental damaged associated with it.

Could food security in case of another global crisis be a good enough reason? I don't know anything about the British situation AT ALL, but I think many in Europe think slightly different about the market-based solution when it comes to both food, medicines, and other essentials after corona.

It turns out that when shit hits the fan, countries need to handle the basic needs of their population themselves.