This is true if not somewhat misleading. Most commercial GMO crops do not target yield but lessens the amount of effort required to maintain production. Similar yields are readily achievable by throwing manpower and tons of agrochemicals at it, however that is effectively a loss of productivity and just as bad for the environment.

Ultimately one can only fit so many plants of maize on a single acre. What is yet to come are GM crops that actually prove the efficiency of photosynthesis and carbon fixing by directly engineering cellular biochemistry, making them closer to the food factory mankind has been working towards for thousands of years.