In the long run that can't be true, when the population continues increasing. There's a practical limit to agricultural yield, even if output can be tripled sometimes. You could generalize that statement as "<unsustainable thing> will improve in the long run with the advent of <thing that kicks the can down the road>". The US debt can be substituted, for example. Always a better solution is to address the "unsustainable" aspect. One shouldn't be fooled into thinking the unsustainable thing became sustainable when the can got kicked down the road for a few decades.
Overpopulation leads to corruption. The situation becomes "every person for themself" to survive.
There's data out there and from what I have read African's fertility rate is lowering, albeit a little slower than some people wished it would. We just have to wait some more years and see what happen. I believe Africa will follow the footsteps of every developing country until now and will have a society of greater urban population and lower fertility rates with economic growth. India and China are still in their way following this path.
To be fair a great number of Indian children still suffers from malnutrition but my argument is that the situation improved because the world is not static as Ehrlich predicted, Africa will also improve in the long run with the advent of modern agriculture techniques.