The Aleutians hardly counts as threatening to take the west coast though.
Side note, my grandfather was sent there. So a battle I have extra interest in.
Anyhow the whole concept comes down to the fundamental problem of logistics. If you posit that Japan could have won, then the question is how? Because technological and numerical superiority only goes so far. The Pacific is a big place, and there is only so many viable paths across. There’s a reason we did the island hopping, so how does Japan threaten the mainland?
Option one involves going through Alaska and downward from there. Problem is they tried that, and were repelled. If that’s the plan, it already failed.
Option two involves taking Hawaii. And Pearl Harbor would have been their best chance. If they truly wanted to threaten the west coast, why not do a full on invasion after achieving strategic objectives there? You have the surprise and we’re able to do good damage, aside from the carriers being out to sea, an invasion right then is their best chance.
Because if you want to roll technological and numerical superiority but supply and resource deficiency into a victory through aggressive surprise, well, half measures won’t do.
So I can’t really take an occupation, or even serious threat, to the American coast as a realistic option.
Any attempt without either occupying or disabling Pearl Harbor leaves a massive vulnerability to their supply lines in their flank. Any attempt to occupy Pearl Harbor had best chance of succeeding immediately post bombing.
I don’t see another viable option, other than the one they tried, which is to dominate and reinforce the South Pacific as best they could. Which they did. And they still lost the war. Because the reality is that even if the US loses Midway, they are better able to absorb those losses and replace. Because there was never a serious threat to the US mainland. The US could fall back to Pearl and regroup much more easily than Japan could push on and attack.
Now perhaps India or Australia would have felt the pinch more. But with China I don’t see invasion or occupation of either area as even a slightly plausible outcome. And that alternate history could certainly change the how and when of the peace signed. But not the why, the why was almost certainly always going to be because Japan conceded.