Density is lower, but daily kWh of solar power per acre stays surprisingly close. In effect flat solar panels are shading each other to some degree for most of the day. Density therefore becomes just another trade off.

Anyway, as long distance transmission is cheap panels are generally on the cheapest land you can find, often sub 1,000$ per acre. This makes minor differences in density largely meaningless. The added spacing also reduces the local environmental impact as plants can grow around the panels which can significantly reduce dust. They also make better use of limited PV manufacturing capacity.

That said, if you’re actually space limited for whatever reason, flat panels win.