Just an important detail that i missed last night. The premise is that the americans decline to fight at Midway, but the japanese invasion attempt still fails. Well, there is a serious contradiction here in that if the americans decline to fight, or just don't know enough to be on time, why would they reinforce Midway in the first place? Without reinforcements the Midway garrison is weaker, less troops, less guns, less planes, no tanks. If they reinforce it as OTL but decline to send the CVs, that again does not make sense as they will send their troops to certain death (they would have no idea whether the garrison will be capable or not to repulse the japanese assault, especially without any support from USN)
Good points. If the US doesn't learn of the Midway offensive, there is no reason to reinforce Midway to historical levels. We then need to look at what would have been normal reinforcements for Midway versus those sent to prepare for the expected invasion.
If the US learns of the offensive, but decline to commit the fleet, how much will Midway be reinforced? It does make sense to me that even if the US doesn't want to risk a naval battle at (what they think is) bad odds, reinforcing the garrison still happens.