Let's talk soldiers + expertise in 5E!

As I progress in what sort of feels like an overarching plan that's been in the works for a while...just needing the proper attention paid to it...I'm trying to make my way through these guys...

On the left is the most basic Cobra infantryman.  On the right is the most basic Cobra infantryman.

...along with some others from my childhood that I grabbed from my parents' house last summer. I'd like to have a nice little stock of figures/fodder to play out battles with, and it makes sense for me to start by fixing up some of my old guys.  With (I'm sure) a bit of a nod to the old OCD, I always took pretty good care of my toys as a kid, so while that means I don't have much in the way of stories about tying them to bottle rockets or YOLOing maximum fun out of them in any way, it also means that picking up a kit to replace their O-rings will go a long way toward setting me up with a nice bunch of gamepieces...

The cure

The happy patient

Old vs. new

As far as gaming goes, I'm looking at really streamlined 5E classes that make an action figure skirmish doable without going crazy from number-and-ability-overload.  Now obviously, for the universe of G.I. Joe, the most important class to have is Ninja.

For now, though...I just want a nice, basic Soldier class that can fit most infantrymen, both Cobra and Joe.  And it seems to me that one of the easiest ways to do that is to just make them experts at fighting, at least with certain weapons.  Like how Rogues can have Expertise in thiefy things, it'd be nice to give Soldiers expertise in fighty things.

I'm realizing, though, that there aren't many who seem to think that doubling a proficiency bonus on an attack roll is balanced.  I guess I figured this would be the case; while 5E's designers did an impressive job taking the unification of combat and skill/tool rolls to the next level with proficiency bonuses (and the elimination of basic attack bonuses and skill ranks), excessive combat bonuses can be a tough sell.  Even if they "make sense," it's often easier to avoid them, just in case.  It's just that...well, it kinda seems like the math for fighting and for using skills should work out about the same at this point.

So why is weapon "expertise" (as in double-proficiency) still seemingly off the table?  Is the bounded accuracy of 5E so precise that a few more points can really break it?  Are there just too many other ways to boost attacks that are unavailable for skills and tools?  Is it forbidden just in case?  And is it time we break this rule and finally grant full, proficiency-bonus-doubling expertise for every sort of proficiency?

Maybe not, but I'll probably try.