To me, the main limiting factor is tent space. In a tent, the yield per plant is irrelevant as a primary measure of productivity. Yes, big plants are best to grow, if you have the space. But I don't think the buds are any less potent or different from mid-sized or even small plants.
I jam 8 plants in a 12.5 sq. ft. tent, about 1.5 sq. ft./plant and generally get about 3 oz./plant or 2 oz./sq. ft. You got ≥12 oz. from 3 plants, ≥4 oz./plant (excellent growing), but how much space in the tent did just these 3 plants take up? To beat growing at 2 oz./sq. ft. rate, your growing space for 12 oz. would have to have been smaller than 6 sq. ft., such as 2 x 3 ft. Fitting 3 plants averaging ≥1/4 lb. each in that space seems unlikely, with plants yielding over 3 oz. each in my experience taking up more tent space proportionately as they hit 4 oz. and higher/plant, suggesting you likely got lower yield per used tent space.