It's also not that far from reality.
They were playing with the idea of a man portable version of the minigun IRL. That's where the idea came from in the first place. The problems with doing so are obvious.
Though we do actually have a proper portable "suit case size" minigun now.
It’s still very much out of the realm of possibility. They tried mounting the M134 onto the Humvee and couldn’t. So the likelihood of seeing a man portable version in reality is still a ways away. Not too mention ludicrous seeing one man using it as if it were possible or practical.
I can’t speak to if the Pentagon was thinking about developing a portable handheld M134 in the 80’s. But, I’m pretty confident in saying that was not the reason for it’s inclusion in the first film. However, I’m open to being corrected.
However, Old Painless is very much the product of its time. Totally 80’s machismo to the nth degree.
I don’t want anyone to think I dislike Painless. I love it. Just something I figured could be argued as an unintentionally funny aspect that could be found in P1.