Questions of endless economic growth are a red herring/off topic.

If exponential economic growth is possible now, then it should be invested in now. If yields change in the future, investment should be reassessed.

"If exponential economic growth is possible now..."

It's not.

You can arrive at many false conclusions by assuming a false antecedent.

I'm not sure what you think is happening then. What do you measure economic growth in, Dollars or percentages?

Regardless of the units you use, you won't get an exponential curve. You can fit an exponential curve to the data. You can also fit a logistic curve to the date.

Heck, you can even fit a linear curve to the data.

This line of thinking can lead to catastrophic consequences if the long-term implications are not well understood. Short-term exponential growth can lead to a catastrophic crash down the road if the debt, resources, or social fractures are not sustainable in the long run.