I have no doubt Welsh land can support many more sheep per acre, but to make minimum wage (£17k) off 71 sheep you need to make £240 profit per sheep per year.

At £100 per fat lamb, you still haven't made minimum wage even if all 71 have twins and you have zero costs. Maybe they sell some wool, too.

In reality you have bills, sheep die, and you need to keep some lambs for breeding stock