Because having to arbitrarily maintain a specific level of heat in order to use your filler combo at full strength is stupid.
That said, there's little excuse for not simply having Hypercharge upgrade your filler combo into "Heated" versions with the same 1.0s GCD as Heated Blast.
It's even worse when you consider the background of MCH lore. A military force that takes little training in order to be effective in combat as an alternative to the years of training to become a good Knight.2. Heated Actions have way too wild animations. It's really silly that everything we do are sideflips, 360 noscope spins, or 720 backflips. And where are the bullets and gunshots?
Imagine signing up for Machinist training in Ishgard, your first day of ever holding a gun:
Machinist Trainer: "Okay, so I want you to get some practice in. Take this and go do a 1080 triple backflip while hitting the dummy over there with 18 missiles"
New Recruit: "...Uhhh..."
Also, on the topic of jank animations:
Barrel Stabilizer. Consists of you tapping on some holographic screens. Makes your gun overheat.
Try and connect any of those 3 statements with logic.
I'd point out that there probably should be something done about how they function if this is to be the case. Otherwise, you're just giving MCH a double DPS CD once they hit 80 and get their second summon.
You also have to be careful to not link them, otherwise it could end up feeling too similar to SMN and their Bahamut > Phoenix.
While we're here, how is it that MCH doesn't have a dragon shot of some kind? Like, for an art developed in Ishgard, that uses fancy tech and aether manipulation... How do they not shoot someone with a Dragon yet?
P.s. If you edit a post, you can go beyond the word limit (I typically write out my entire post then Cut 90% of it and Paste it back in an edit... As I may be somewhat verbose)