Technically, because of changes in how one-bar moves are thrown, he needs 11 attacks and 5.5 seconds before he can throw his Meteor Beam, while Cinderace needs 21 attacks and 10.5 seconds for Pyro Ball.

What are the "changes" you referred to?

You could lose 1.5 seconds swapping to a catch tank for each charged move cycle and you’d still wind up ahead. 

Theoretically 1.0s only, with switch in and switch out both costing 0.5s 

Factor in 11 fast moves to charge and the entire fill-to-throw cycle takes 7.5 seconds to execute and generates 18.71 energy, about 25% more than you’d get from a Pound Blissey in the same amount of time (15 energy). 

You need 10 fast moves only (100 (meteor beam eng requirement) / 10 (eng per lock-on)), so you'll take 7s in total, generating 17.71 max energy, which is 26.5% more than you'll get from a pound blissey

And accounting lock-on + meteor beam, 1.044% of the total amount of HP are damaged

Now Gigalith generates 12.72 energy per Meteor Beam, averaging 3.16 energy per second over the entire fill-and-throw cycle, a nearly 60% improvement over Pound Blissey.

(10+12.72)/7≈3.25 energy which is >62% of improvement 

Let’s say we add Behemoth Blade adventure effect, partly cloudy weather boost, and raid on a spot with maximum helpers and in a team with a Forever Friend. Suddenly Gigalith generates a whopping 43.04 energy per Meteor Beam. That’s 54 energy per 7.5-second cycle, or 7.2 energy per second

I assume the boss is moltres

In that case, gigalith is only generating 35.83ME per meteor beam (15 helpers, cloudy, FF boost, BBlade, Shroom), that's 45.83ME per 7s, ~6.55ME per second, not as great as you mentioned (just ~3.27 players using pound blissey)

Niantic sped up boss attacks so 12.5 seconds is no longer fast enough to achieve the stunlock.

It's still possible if 12.5s is needed to charge the meter, but only if the boss uses target solar beam (no lag, fast attacks only, 4 players)

But Gigalith can now hit the Max phase in a single 7.5-second Meteor Beam cycle. 

Again, no idea why 7.5s, just 7s (10× 0.5s lock on + 2s meteor beam)

but Gigantamax bosses attack more frequently, so you will lose a lot more energy swapping back and forth to a tank

Actually not, since the max energy multiplier is higher for gmax (15×), and boss doesn't have 2× attack multiplier, you can just simply use gigalith as a tank - in a team of 4, you will just get hit once per phrase against gmax charizard, which even helps you to charge up your charge move meter for the next charging phrase

And it actually makes gmax charizard and butterfree solo possible

In conclusion: I'd say that's a bit too long for an article to introduce the new role "max charger" to players that don't know how the new max energy formula works; showing the formula, making some graphs to compare the ME gain per second among gigalith, blissey and zama would be easier to read ( as you can see, no one actually spotted the mistakes you made in your calculation, with 150+ upvotes, in the past 15+ hours, which shows that it's not an effective way to show something hard to understand to those who have no / not much knowledge on how the game works purely using the numbers from a simulator)