I get your point on parabolic v. exponential... it all depends on the time scale. Any exponential growth will depend on the resistance v. the motive force for growth. in time resistance will defeat motive and a flattening of the curve will lead to a decline and a parabolic return will occur. Then commences the next parabolic cycle. So your argument is probably correct in the longer time frame but misses the fact that this cycle has only just begun.
Such turning points as you suggest are usually innate and so global warming is likely to be the best indicator of a turning point. Covid is an extraneous influence that will eventually form its own cycle as described above, but the human species cycle will be determined by our own motive force and the resistance established by our own effluent which poisons our environment and leads to decline, i.e. GHG emissions... Unless of course, we as a species can either learn to reduce the resistance to our existence by our effluent or develop additional motive force through mutation/innovation to adapt to a changed climate.
50 year's ago we had a similar crisis with industrial pollution especially H2SO4 which was threatening our ability to grow foods. The global community combined their efforts to reduce such pollution and our world became less threatened and our food production methods improved as a consequence. This is a prime example of the motive force overcoming the resistance. Global warming now forms the new resistance phase.
