That's true, we evolved to adapt to calorie scarcity but our environment has changed: calories are now abundant but our system is still optimized for scarcity despite that constraint no longer existing. I'm sure in a few thousand years that'll go away (possibly faster, as we get better at manipulating our own biology) but the status quo is that we're poorly adapted to our environments, energy-wise.
In an energy-rich environment, evolution should select for faster and faster reproductive rates.
Perhaps so, but humans are reproducing later and having fewer offspring, so there are more variables than just energy.
Environmental stresses are well-known to cause reproduction rates to plummet. That can be because of a lack of available food, but it can really be any sort of stress.
Excellent point.
But note that calories scarcity is a simplistic model.
What I'm trying to show with what I was saying, is that there are stocks of scarce molecules imposing performance limits too.