Here is what I know about the reef tank hobby - it is the only recreational activity that I know of that has just as much people posing as "experts" as scuba. And just like scuba, they drop names and drop their years of experience as if that gives credibility to their arguments. And just like scuba, they resort to logical fallacies to support their arguments.
Despite your ad hominem attacks, I am not particularly motivated to illustrate for you what you clearly refuse to see. But to humor you, I will give you just one example. You state:
If that diver puts together a set of double 130s, fills it with 32% and wants to dive this rig to 100ft (30 meters) in the ocean while wearing his 7mm farmer john. Is this a good idea or a bad idea? What are the gotchas for this dive? It's not a hypothetical. I've watched someone do this.
P.S. My only experience with triple, quadruple and quintuple (is that how you say five?) tanks is using stages and deco bottles with backmount doubles. These configurations are not that uncommon in tech and cave diving. I have no experience in sidemount, independent doubles or the convoluted set ups that world record depth divers use.
Anyway, my position on it is this, someone who doesn't have knowledge and is wanting to do dives that require 3, 4 or 5 tanks, it is absolutely imperative that the diver get proper training.
You failed to give an example. What you described was a hypothetical situation, not a basic principle, an important skill that any certified diver should possess.
In your example there are a number of issues that might present problems, including the implications of the gas mix, potential for exceeding ND limits, especially with that much gas, possible buoyancy issues, all sorts of things. This is not relevant to what I wrote. You might just as well have thrown in other irrelevancies, like the possibility that the purely hypothetical dive was at night in freezing cold water in a current with a powerful down draft at the edge of a drop off where terrorist frogmen armed with sharp bamboo stakes stalk any diver with more than one tank because such a configuration is an affront to the Goddess Iemanja, and that the diver, though fully certified, was suffering from senile dementia and had just consumed an entire pepperoni pizza before entering the water and was using a bowling ball as his primary weight system.
Hypothetical examples are infinitely expandable and cannot substitute for technical analysis.
Eng is dead. He was never famous. There are, in addition to scuba and reef aquaculture, many areas of recreational activity in which people pose as experts and drop names.
"Dropping their years of experience" would be counterproductive, though, since doing so would diminish the pretentious affectation of the poseur who was attempting to impress others. Adding, not dropping years, I would have thought. Another logical fallacy?
Why stop at quintuple tanks? I wonder what you think about the possibility of carrying a bag filled with 30 or 40 Spare Airs to be used sequentially? See any problems? Would further training be in order?