In what world is lab-grown meat production more efficient than cattle farming?

Hard to say now if it will actually be MORE efficient or environmentally friendly, but initial indications once price parity is achieved would lean to YES. In terms of timeline, reports show at least 5 years before it can hit the grocery stores and that doesn't take into account the regulation. Here is a good resource that shows the process, companies making it, etc. https://cellbasedtech.com/lab-grown-meat

Given enough resources to refine the process and a few years, I don't see how in the long run it cant become more efficient than farming.

I don't buy it. You're comparing the energy inputs required to support large-scale tissue engineering operations with those needed for grazing cattle on pasture. It's not even close.

If it was just pastures I would agree. But 30-40% of all corn produced in the US (the largest corn producer in the world) is used to feed lifestock [1]. That's a lot of perfectly good farmland that could directly produce food for human consumption.

Even if the lab process takes more energy, as long as producing the growth medium takes up less farmland that is a win towards the goal of having enough farmland to feed the world.

1: http://www.worldofcorn.com/#corn-usage-by-segment