The bulkhead seats on UA, especially the 757, are not very good in terms of legroom. Although '2 inches' is a ridiculous statement, it's true they aren't very good.
The rest of F seating on a UA 757 is WAY better in my experience than any US configuration. Miles ahead. I have several E+ seats on UA that I would prefer to US F.
Your list of 'Cons' are nearly completely linked to routing or aircraft type:
Cons:
From BOS-ORD, a 2.5 hour flight, there was NO food or snack served - not a pretzel or a peanut.
This isn't supposed to happen, sorry it happened to you. Comparing same flight times and lengths UA is much more likely to serve meals than US.
Bulkhead seats on the 757 have 2 inches of legroom - you're locked in place like in a torture chamber.
Bulkhead on 319 has a cutout, but you can't put your legs up like you can on the US 319/320.
Airbus F seats not as comfortable as US airbus F seats - headrest wings don't "bend"
Only 8 F seats on the 319 so reduced upgrade opportunity
UA bulkheads are bad, I haven't compared them to US bulkheads as I don't like bulkhead seats in general. But unless you really need a bulkhead, this is not the majority of F seats.
This is also comparing UA's worst mainline F aircraft with US, on UA you can often find a domestic 757, 767, 777, as part of your routing, which is much preferable to the Airbus.
So yes, take UA's worst and compare it to US, it might be 'comparable' or just slightly better. This doesn't show US in a very good light.
What is the Economy to F ratio of UA's A319 to any of US's reconfigured planes?