While obviously true, theoretical knowledge vs practical experience means something here. The fact that it worked with the 1st infestation (which was massive) & not the 2nd means something -- as does other's experience with mites.
For the aphids on the D. regia, I probably did the CO2 3-5 times (which was a major pain because the supplier was 45-60 min away). Since plants will use the CO2 to make oxygen in the presence of light, unless you black out the tank, you're limited to a long night's worth of O2 deprivation. In addition, depending on how much material in the tank (media, live LFS, etc), complete displacement of O2 with CO2 may be potentially difficult (as is knowing if displacement is complete). I have no idea why the process didn't work the 2nd time with aphids - but it wasn't for lack of trying.
I had no experience with the mites but based on multiple frog people reporting their results, the process didn't work with them. A buddy had read that they may enter a state of torpor where they can basically shut down for a period.
I agree that a fully furnished terrarium presents complications as far as complete displacement of the air. But one thing to consider about multiple treatments: if you do it every day for a month, but the eggs of your target pest take 31 days to hatch.......as in any fight, knowledge of your enemy is your most effective weapon.
Judge not lest ye be judged creates a cesspool. Judge others and prepare to be judged by them.
Just know when to keep the verdict to yourself.