While the Japanese may (or may not) be concerned about the two turrets, their problem is they can only augment Wake at the expense of something else. A ship sent to Wake can't be someplace else at the same time, and now to go elsewhere for a subsequent operation has a long slog. IMHO if the Japanese know about the turrets and have a concern, it is more likely they would try and deal with them with air (dive bomber with AP bomb). OTL the Japanese had a huge amount of luck, spreading limited assets in so many directions. Here the Japanese have no more assets, and every place that was due for assault from PH onwards is going to be a tougher nut. This could be better training, earlier use of assets (like radar in Hawaii), more forces, stronger physical defenses, or some combination of any or all of these. Best case, almost ASB scenario, for the Japanese is that they achieve most of their OTL successes. Even under best case results for Japan, the cost in sunken/damaged ships, aircraft losses, personnel losses (including valuable aircrew) is going to be substantially higher than OTL. Thus the downward spiral for the Japanese begins sooner. Of course if the gains with these higher losses are less than OTL, the spiral is tighter and faster.