Here's where the 66.66% figure comes from.
Flameburst + Rapid shots is 3 seconds (5 Heat Regen a second)
Flameburst uses 16 Heat, and gains 15 heat (5 heat regen for 3 seconds). Net Loss: 1 Heat.
Ion Pulse uses 16.666% Ammo, and gains 15% Ammo. Net Loss 1.6666 Ammo
Vanguards lose 66.66% more Ammo for every Ion Pulse (assuming the filler is included)
Go Test it yourself for once and you'll see the results. Any random lag is going to affect both characters equally. Want to reduce randomness? Run multiple tests, average the results.
First off, by adding rapid shots you are simply subtracting from the numerator of a fraction (heat loss/time) thus making your ratio of those fractions (vanguard/merc) absurdly high. It simply doesn't help your cause when you inject math distortions like that and then trumpet the result, "Vanguards use 66.6% more resources than Mercs" which fails everyone's basic understanding of the matter. It's like claiming that wine has 10x the alcohol content of beer - if you first extract a fixed amount of alcohol from each fluid.
Secondly random lag doesn't affect both characters equally. It affects the mean (average) performance of each character equally. That is a statistics distinction which you may not be aware of. But your testing methodology is specifically vulnerable to random white noise, for reasons which I will try to explain. The basic segment of your test (FlameBurst + Rapid Shots) has almost NO measurable heat usage (1 unit). Over those two GCDs, your timing loss can easily be 0.2 seconds, which causes heat dissipation of - yes, 1 unit! Thus a common level of variance can completely disguise the very metric you are attempting to measure. That is why a test consisting of basic segments with a higher measurable heat usage, such as I used, are inherently more accurate.
Yes, you could get more accuracy by running the tests repeatedly. But using your methodology you might literally need to do it hundreds of times because the variance is so high relative to the mean of the metric you are measuring. Good luck with that.
If you do not think what Holmes did is a valid test, suggest one so that we can prove we are correct.
Sometimes, no matter how hard both people try, it is not possible for the person taking the other side of an issue from you to prove that you are correct.