I think number of people killed by a sometimes fatal illness is not an unreasonable thing to track and use as a metric of success. And many more than 1/1000 of UK citizens have had it already (where did you get that number from) - that would be 60 thousand people, whereas 152k in the UK had it at the end of April [0]. There are many benefits to pushing back the peak so that we have improved capacity, learnt better how to treat it and moved closer to an eventual vaccine.

[0]: https://assets.publishing.service.gov.uk/government/uploads/...