First, as one of the pioneers of colubrid breeding, we did not come up with power feeding. That was something people without experience labeled things they did not understand.
In the old days, we did not have shoe/sweater boxes to keep snakes in, so in our ingnorance we used large cages and actually included subfloors. What this did was allow a large range of temps. From too hot, to very cool. We also were not fortunate enough to recieve advice from other hobbyist, so we actually looked at natural snakes for advice. Here we found, they included a range of temps to accomplish different life tasks.
You really should remember or think about this, There was no market for snakes when this husbandry that allowed reproduction started. They were for all intents and purposes worthless. So, the commerical aspects so commonly assigned these days, did not exsist. It was a labor of love, not money.
next, you fail to include the proper details. Snakes did not grow fast and breed at 18 months and multiclutch, because of heat alone. They did so, because they had a range of temps. We were actually so dumb, we often went overboard in all directions. Again remember, there was no "recipe for beginers" to follow.
As for your narrow temp ranges, I have to wonder if that is not a product of being commerical. As i see it, you simply cannot include a wide range of temps in a shoebox. Therefore the shoebox predicts your temps, not the snake. The commerical part is, you can house literally hundreds of snakes in shoe/sweater boxes, where that would be very difficult with large cages.
With our field work, we see on a daily basis a range of temps, normally from 18c to 37c. These temps are rectal IB temps. Normally a temp of 18c tells up the snake has recently imerged. Body temps of 37c tells us the snake has been out a while. FYI, these are for basking snakes, not crawling snakes. That means the IBT is for a use. As the years passed we started taking throat/head temps, to compare to rectal temps. We found it very rare that the two were the same. At times they were as much as 10F difference in one individual.
Feeding in nature, snakes are pulse feeders, they feed heavily for short or medium periods of time. The rest of the time, they either reproduce or conserve energy. In nature, I have seen neonates grow to maturity in three months. That is something I have not been able to accomplish in captivity. The reason is clear. In nature, they either conserve energy or expend it. Normally they are not stuck in limbo(shoeboxes)
Once you take this usable range of temps away, you will witness all sorts of problems. Including all of the things you mention. The problem I see, as one of the oldies is, you are now overmanaging reptiles. You have taken away there choices. But unlike the monitor folks, as least you are successful. With snakes, we can discuss shape and such. As breeding is commonplace. With the monitor folks, they argue the world, with no or little success. Yet the problems are very much the same. We are working with reptiles, their required temps are task dependant. They require different temps for different tasks. Its very simple. They are not endotherms, which may be better understood as constant temps. As opposed to exto-therms, that are not constant temps, but variable useable body temps.
By the way, I never had problems with young reptiles reproducing. In fact, I have not heard of any records that surpass so of the results we had 30 years ago. For instance, I had three 18 month old Blairs, produce 66 healthy living offspring in one spring and three 18 month old Calkings produce, 99 offspring, in the same time period. All of these females went on to live long healthy productive lives. Most multiclutching well into their late teens and then living for many years past that. Even successfully reproducing after that. But not consistantly. More FYI, on our studysite, we commonly find young gravid females, some with a button, a rattle and a base. Thats two sheds. In captivity, that would be about four months old. But I think in nature, that is last years babies. Again, on our site, most of the reproductive females are tapered rattles, young. It is very rare, I am not sure I even remember, a strait rattle female being gravid(old female).
Congrats of your successes, but you should actually research more. Your opinions of what happened in the past are reasonable, but not accurate. F