Why didn't they make the Samurai a heavy armored counter-attack tank?
Why did they give the Scholar a pet?
Why is the Dark knight not using his health to deal damage?

Because every FF universe is different and there are restriction lorewise and gameplay wise.
For instance, the job was created in Ishgard in FF14. They do not use Chainsaw and Drills. They're fighting dragons. When it comes to taking down a flying lizard, a gun is more suited than a chainsaw.
We don't acquire the job in Garlemald (or from someone working formerly working for them), we acquire it in a land where the only useful technology is a technology that kills dragon effectively.

My only disapointement with MCH is the lack of goodies. I was expecting a bit more interaction on the turret departments because the turret was highly advertised.

Perhaps in 6.0 they'll add your gunblade job with all your techno stuff.