The main problem with the kill-USA strategy as I see it, and perhaps where there is opportunity for dscussion, is that there are little rewards for the Axis if they fail in their ultimate goal of taking Washington.
In other words, the Axis powers are rewarded with both territorial IPC and NO gains for going after the other Allies. An attempt at Moscow, although it may fail, will at least gain some IPCs for the Axis. A failed attempt at America could leave the Axis with nothing gained for their massive effort.
I would suggest that the Axis need one if not several secondary objectives to pursue should they fail to capture America in order to make the strategy more successful. For Germany and Italy, a strong push West in the early game should net them control over Gibraltar and the Med. Another benefit is that the required strong Axis naval force will keep the UK defensive. Japan should probably focus on removing as much of the US pacific income as possible, and should still take the DEI in order to finance the war effort.
A more fanciful idea would be for the Axis, in a scenario where they have deployed heavily, but are unable to take Washington, to instead drop their forces in South America. This could be part of a global neutral crush strategy…or the Axis could pile everything in to Brazil and use DD blocks and their existing forces to build a minor.