Maybe not across all departments, but in the fire service, there's pretty reliably one single standard.
The hoses weigh what they weigh. The ladders are all the same length. We all had the same physical standards and tasks to complete in order to be qualified for our positions. Doesn't matter where your dangles lie. Lightest women had to recover me on a denver drill, as a prime example of doing full on worst case scenario. A
Denver Drill is basically a rescue through a shoulder width window with about 7ft of space lengthwise, shoulder width otherwise, and a downed firefighter. It's not easy by any means, but it's accomplishable. It sucks even when you're all same size. 2 150 lb bad ass ladies did that. They also had to do full building recovery of me (At the time, I was the biggest guy in the department so in lieu of a dummy, we literally trained on worst case scenario rescue/mayday drills.) to include below grade.
If anything, I had it easier because I had the vast reserves of Ranger/Sasquatch strength to call upon.
I fully support a single standard for a job. I think that there should be specific unit requirements laid out by DA, in order to maintain unit cohesion. Example being Ranger Regiment. Doesn't matter your MOS, there's the Ranger standard within the Regiment. Mostly because there's only..... 4? Maybe 5 now? noncombatants IN Regiment, and that's the Chaplains. At least in the incipient GWOT kickoff, everyone had a combat job. Don't need to detail them all, but everyone got their hands dirty in one way or another.
That standard cohesion means that as a rule, while you might not be able to fully swap positions between a Cook and an Infantryman (Unless the cook's Tabbed, in which case he's got more 11B in him than a private out of 11 series OSUT honestly), you know they'll be able to hang and with RASP, everyone will have a minimum standard of training as well.
Doing the same for all of the 101st, 82nd, etc, as far as it can go with Line vs Support vs CSS, would honestly improve the force as a whole. You'd be able to draw the line in the sand and either reclass or just remove those that didn't meet the standard. One thing you would also have to do is address promotion competition as well as manning through an actual increase in MOS'es through identifiers. A "soft-skill" in Ranger Regiment, for example, shouldn't be competing against full rear-gear soft-skills in say a FSB, for promotions, because they're not held to the same standard. The points system and requirements would need to be adjusted off of those identifiers, just like it's off MOS now.
Implementation of the standards would have to hit army-wide at the same time, and "offer" an Up route if people qualify for a higher (more direct role unit) position, and a regressive role for those that don't meet the standards. Physical would be the big one, but you could implement further standards as far as requirements for PULHES and line scores on the ASVAB at a later date.
It's not to say you want all the fat idiots in the rear at all.... but for those who are most likely to be shooting or punching the enemy in the face, it sure would be nice to put your best foot forward in that regard.
I also think that there should be a larger framework for retention. Especially those that self-identify that they have problems and work towards trying to rectify to the best of their ability. Plenty of roles in the Army, let alone other services, are non-deployable and would be fine places for those that wanted to continue to serve, either enroute to full capability or in a redirection of skill and drive. That's another discussion though.
