First of all, thank you for you're very well laid out response, you're truly a great member of this community.
Most of the time (75% by my estimation), Hell give at least 1 Gold Chest per run. The rate to get Gold chest on a spin is a lot lower than a Brown Chest, so normally, you would usually get all your Brown chests and would stall on 5-line spins for a long time to get the remaining Gold Chest(s). So, by trying to save on revives and use a dual Dragon Queen setup would usually mean wasting more revives trying to stall for Gold Chests, or you would end up killing Karen without even getting max chests and that usually means no Gold Chest as well. In the long run, you would end up using a lot of Energy Potions (keep in mind 50 energy is half an energy potion) for a lot of Fairies and Spiders and very very few gold chests that most of the time end up as Pinocchios. If your goal is just to try your luck getting 1 Karen from Hell with the least amount of revives possible, then your way might work but it will be incredibly frustrating and possibly might not even get you a Karen in 2 weeks. Keep in mind, the odds are severely stacked against you so you will spend lots of time and energy potions compared to other people just to get a Karen.
Otherwise, if your goal is to max skill a Karen, then you should try to find the most effective team you can for farming Karen and try to get max chests as many times as possible because that increases your chance of scoring a Karen and because only Karen can help you skill a Karen.
It's fairly well proved that the rare gold chest card drops much more frequently in Hell then in Insane. While Karen might drop slightly less often than Pinnochio in Hell the odds are not as drastic as you seem to be implying, I'm guessing 1 of every 3 or 4 gold chests will be a Karen in Hell, and Insane it would be 1 of every 9 or 10. I don't know what the exact odds are but I can quote PM as saying the rare gold chest cards are easier to obtain in Hell than in Insane. I got Karen on my second run through hell, most players I know are able to obtain Karen within ten hell runs. Usually Insane takes many more runs to obtain rare gold chest.
As for you're suggestion on farming Karen. I simply don't see the cost/benefit of even considering it. I'm sure dark and light wonderland might make more sense as Pinnochios from those levels can be used to skill up useful skills but unfortunately moderate fire damage isn't that useful. Unfortunately if you saw my cards you probably would agree with me that dual DQ is the best team for me to use. I'm a PPP and blue panzer can't be used in this map.
Also I'm not sure if I agree with your understanding of how chests drop, I don't think any particular spin is capable of yielding either brown/gold as you suggest but what I've witnessed is that the color of the chests drop in a predetermined sequence initiated with the start of the level, so for example I might get 2 brown chests quickly, grind for a very long time and get a gold chest, then get 2 more brown chests quickly, or maybe I grind for a long time and the first chest I get is gold, then 4 more brown chests very quickly. I usually witness this when running Gem Dragons on difficult. Spinning for a long time till the gold drops then browns follow quickly no matter what position gold chest drops in.
Lastly, I'm fully aware of how Boop was able to max skill a Faith, by being an extremely dedicated player with extremely good cards at his disposal. What I'm asking is if high level players feel it worth farming hell now since it seems the difficulty has increased. If people are farming Pinnochio, what's their preference hell, insane, or difficult? I mentioned Boop's example because I believe I'd be willing to put forward the same amount of revives, also the same amount of time, but I feel the difficulty of wonderland hell is too hard to make this possible.