Every game has its flaws and gaps in logic.
Why don't the Seals in CoD just bring in a tank from the beginning and wipe the floor with the other team?
Why does the Australium elevator in TF2 move so slowly?
Why doesn't Conner die from falling from so high in Assassin's Creed, even if he does land in a bail of hay?
There are a million and a half "If video games were real" videos on YouTube, and they are fairly entertaining. The overlying joke is, if video games followed the rules in real life, they would be stupid and no fun.
When it comes down to it, it's a game.
And a game that's no fun has no point in being played.
HOWEVER, that doesn't mean your ideas are broken.
It just needs a little (here comes that word) balancing.
Anyone remember Star Wars: Battlefront 2?
Really? Just me?
Okay.
Well, there was a class in that game called the "Clone Commander." He had a heavy gatling gun that could rip through the enemy droids like nobody's business.
However, this gun had downsides.
One, it was HUGELY inaccurate, only able to kill things from the sheer output of bullets.
Two, it took a while to spin up. Not Heavy's gun from TF2 spin up, where you can push a button to get it ready.
This gun's firing button and spin-up button were one in the same, causing you to waste ammo and give away your position if you tried to spin it up early.
If we were to implement a Heavy Gatling Gun here, it would have to be inaccurate (so it couldn't be a sniper with the Heavy Flak) and take about 5 seconds or so to spin up (so surprise attacks would be viable to take them down).
That's just my take on things.