Oh, no big deal on the discussion... I take no offense...

Well, without going into too much detail, I think you are oversimplifying the way water currents work and the way any body of water reacts to not only currents, but how debris within those currents get filtered out...

Honestly, I think two skimmers AND main drains would be beneficial in a pool where you have debris making it's way in (such as trees/excessive winds/etc)... Now is a second skimmer going to make a 100% difference, no. Will it make a 30-50% difference, for a pool with lots of floating debris, sure.

Now, for me, the big issue for main drains is not for just the ability to drain the pool. It is for all the reasons I stated above. My pool stays cleaner, there is always good flow regardless of how full the skimmer gets, and I have great equalization of temp throughout the depth because of the constant pull of water from all areas in regards to heating.

In regards to debris, only some debris will float. Only what floats will get sucked into the skimmer. Anything else that falls to the bottom will stay there, unless it gets sucked into a main drain. Now, does that mean that all debris that falls to the bottom goes into the main drains, no. But, from experience, a substantial portion does make it's way either into the main drains, or close enough that while vacuuming it is easy enough to push whatever will go into the main drains and whatever is left actually gets sucked up by the vacuum. ie, the pool is much cleaner with less work with a main drain compared to not having one. I must also point out the folly of assuming that you have full circulation if you only have a skimmer and the skimmer basket gets full. That is far from my experience with large leaves that get sucked up in my installation, as it is obvious that when the skimmer gets full the majority of water gets pulled from the main drains by way of the amount of floating debris that still exists on the surface, yet when I cut to only pull from the skimmer in such cases I get a huge reduction of output from the returns...

as far as draining the pool, there is a huge difference from using a main drain with 2" piping and a submersible pump. The main drain allows for full pipe volume in draining, with the pump only allowing for the max hose size you can connect in draining. Apples and oranges in comparison, since there isn't any. It took me all of 30 minutes to drain the pool enough with the pump running and the main drains cut in exclusively. With a submersible pump I would have been lucky to do the same in 12 hours. There is a massive difference in volume between the two. Opening a return is only valid if you wish to flood the immediate area with chlorinated water, and even then you wouldn't have the speed of using main drains with the pump running.

I do agree that a lot of dirt settles to the bottom and stays there, regardless of how many returns or skimmers/drains, so you will always have the need to vacuum the pool at times (or use an automated pool cleaner), but I can attest to the fact that the pool stays way cleaner with main drains running along with the skimmer overall, so cleaning via vacuum/automated pool cleaner is reduced in all cases, especially in mine.