When you do things well 50-70g/sq ft is about as good as you can do with ambient co2 and a controlled environment. I wouldn't count larfy, airy buds in this metric, but some people have a need to measure from their taint.
from-seed is going to be volatile. you get a herm and obvioulsy that hurts, but other genetic variety can cause a weaker yield too. If plants develop solid nugs and you don't over-crowd the canopy, use 50g/sq ft as your minimum goal... if one plant is weaker, that obviously hurts yield potential. Use clones of known monsters if you want to maximize yield per sq ft.
that plant is only using half the space and looks a bit on the small side. Maybe 50g dry, give or take?
controlling climate at least to some extent, healthy plants and proper canopy management will get you there. You don't have to do anything extravegent, really. You can pay 30cents per gram produced or 2 dollars per gram produced, up to you on that part, lol.