We started WWII with some inferior equipment but not all of it was that bad.
Our planes were a little bit behind but not as bad as many think. I would guess our ships were about as good as any and our service rifle was the best of any tho it was a year or so until they became plentiful. No big deal as the 03 Springfield was still as good as the Axis guns.
Probably our tanks were rated the worst but I remember seeing a Arika Corps veteran saying when the British got large numbers of American Grant and Lee tanks, they were better than what the Germans had.
I think the one thing the Germans had over everyone was the 88mm artillery.
Actually, our M4 Sherman was the match for the Mark IV German tank and better than their Mark III, which was their most plentiful tank. these were the tanks we faced in Africa when we started fighting over there. The M3 was not a good tank, the main gun was fixed and could only be aimed by turning the tank. In other words the Grant and the Lee were both inferior to the German tanks of the day. The Sherman was not.
However, when we got to Europe we were now facing the Mark V and Mark VI, the Panther and Tiger.They were both superior to the Sherman. They Panther had the same size gun as the Sherman(75MM) but it was a high velocity gun, better than the low velocity gun the Sherman had. Plus the armor on the Panther was better. The Tiger was so far above the Sherman that it speaks for itself.
Our big advantage lay in the fact we could produce hundreds of Shermans to every Panther and Tiger produced.
Typically, it took 4 Shermans to knock out one Tiger or Panther. The Panther was arguably the best medium tank of WWII, better than the Russian T34, which inspired it's design. The Tiger and the King Tiger(an upgrade of the Tiger)were both too heavy for the Power pack and were prone to break down frequently.