To be clear, there is nothing great about genocide. I only agree in the capacity that Earth cannot sustain seven billion people not because of lack of resources or landmass but the lack of maturity.
All humanity's attempts to control the population will fail. It may fail over decades, centuries; but ultimately it will fail. The only thing that will successfully contain the population is disease and natural disasters. Wars do NOT contain the population. If anything, they seem to increase it. Billions die in a war, but even more billions are born after. Why? Because of humanity's instinct to survive and when humans feel their lives are in danger, they usually will copulate.
Over population is not a myth, however. It is subjective. No other living mammal of our size on Earth comes close to the population we have today. That can be discerning. The only mammal that may rival our population size are rats. Insects, though, ridiculously outnumber us. Ten trillion to one.
I'm not saying you're wrong that if we lack "vision", or what I call maturity, to grow our resources, we could sustain seven billion. Possibly seven trillion. But we don't and we are at the highest point our population has ever reached in the history of the human species. There is no precedent for this level of resources to human sustainability. We are overcrowded, too unintelligent, too radicalized, and too violent to have that kind of maturity to sustain this level of population at this time. The fact that we have leaders who consider genocide as an acceptable alternative to advancing renewable energy validates my argument.