I don’t think exponential population growth is a myth. What you pointed out - the decline in the population growth rate, can be interpreted as the result of interventions (provision of birth control, better education) that has mostly dealt with the issue. If you even simply stuck with what Malthus said, the point is not that population will grow forever, but rather that it will eventually become limited by one way or another - and either that’s by controlling the birth rate, or its by widespread famine leading to mass deaths. The population projection is really about the pressures on the system.
That doesn’t mean there never was a problem and it certainly doesn’t mean we wouldn’t be vigilant in the future.
