Those are certainly good points, but it is not that the US is going to take EI, it is that you are never going to need those (4) build spaces for Japan. Or more accurately, be able to use them every turn.
The problem with the factory is you are ultimately going to have to defend either Sz 37 or Sz 60.
The US can pretty quickly go to Mid or Ala (say US 2). Then you go to Wake (US 3). Very quickly Japan sees the US coming at them an must counter. And once Japan counters with additional ships or air, you don't need 12 build slots and you won't be needing to place tons of Navy in Sz 37 at this point b/c the US can have a token threat on Japan.
Again, I'm not saying Japan will fall or EI will fall, or the US will sink the J fleet anytime soon, what I'm saying is you spent 15 ipcs on something that:
1) You won't be using for its intended purpose (crush india sooner) or using very much at all
2) You won't be needing for added build slots since planes and possibly ships are more expensive than inf and rt.
I think the safer play is to just to wait until J2. Yes you don't get to India any faster, but you also get to see if the US pulls out of the Pac or how they plan to play on US 1.
Personally I don't like putting the target out there on J1. It just invites a scenario where you feel obligated to defend it and you end up not placing a bunch of units down there as the US builds up its navy and moves out into the Pac.