1. If you put your idea like that, yeah, makes sense i like it. Cant argue with that, would make an interesting addition to mch
2. I dont really think that problem of weaving mid heatwaves happens unless you have 1+ charges on any of those, or if cd left on one of those is less than 15-20 seconds. At least from what ive played, if they are freshly cd-ed , you wont really need to weave anything in 1.5s window. Altho i would much prefer heat waves to not reduce gr and rc cooldowns and increase potency of those twofold (as an example)
I dont know about official forums, but on reddit there was a lot of stuff like "MCH needs complete overhaul", "Devs should bring it back to drawing board" and stuff like that. Plus iirc yoshi-p on one of live letters said that they will be able to do reworks of mch and mnk only in 5.0 even though high demand for it was there (not so sure about monk, but i remember it being mch and some job that didnt really need any adjustments)
3. MCH being simplified is what made this job have 3-4x more players on it as opposed to how it was on stormblood (comparing between fflogs omega savage clears and eden savage clears). Cant say its bad result.
On matters of overheat and wildfire. You didnt put 6 gcds in wf. What happened is you put 6 gcds in overheat, 5 of them in wf. You never do wildfire outside of overheat.
When you overheated with flamethrower you would instantly cancel it with first gcd, then you would apply wildfire and then insert 5 more gcds (with rapid fire). All and all, last gcd would enter just almost at the end of overheat, with all that taking 9.5 seconds (if your gcd is 2.5 seconds) out of 10 seconds of overheat. Any small mistake with weaving or luxury of having ping issues (applied to mch it meant you didnt live next to the server) would make you land your last gcd out of overheat.
Overheat is 20% damage buff, wildfire is glorified 25% damage buff, so if i dont suck at math, it would make up for 50% damage buff (excluding hot shot, with hot shot its another 8%). Most of your damage on mch comes from overheat, so if you cant put all 6 gcds in one overheat with all ogcds, you should just go and play bard. Great forgiving mechanic btw.
They could of course fix it (and i would like to see how they would fix it, idea of sb mch was really great, but was gone deep down in the trash can in practice), but i think at that point they thought that better to just "get back to drawing board"
Most popular suggestions were actually brought into the game, no matter how you look at it. Rifle Tumor (aka gauss barrel) was removed, wildfire is fixed, button bload reduced, job itself is streamlined, clunkiness reduced, reassemble is now direct crit, there is actual good aoeing now (crossbow, flamethrower and bioblaster make aoeing stuff really satisfying, spread shot is not sh-bad anymore). On top of that, machinist is actually machinist now, and not gunner.