It does seem like daily XP gain limit is a mechanic not thoroughly thought out. It seems like a kludge for not properly scaling XP gain. It may work for land and air, where engagements can be long and drawn out, but naval combat is 95% waiting and 5% total annihilation, which pairs very badly with XP cap mechanic.
More generally, I think XP gains for everything needs to be rethought from the ground up. For pretty much every one of the six combinations of branch and training/combat, you either get too much XP or too little. For land combat, XP is too hard to get in general, especially if you don't engage in meat grinding tactics. For air, XP is too easy to get from combat and too hard to get from training. For naval, XP is too easy to get from training and too hard to get from combat.