The decision to go with this, along with several other choices, kind of made more sense to me when considering how the devs are hoping to maintain the early game meta. Very much seems to be based on allowing the players to get accustomed to several features, be it the amount of perks you can play with, the guns that are available or even things like the game's controls. It surprised me how incredibly perk-and-gear driven that Splatoon is, almost moreso than TF2 is.
And by those standards I think that having a rotation of maps isn't a bad idea in theory because it means that most players are incentivized to actively explore how to best apply the metagame, what works best and so forth.
The only issue I have is that four hours might seem a bit... long, at least when you think about it. I'd like to hope that the more maps we get, the shorter the time will be. I could see 3 or 2 hours work for its benefit more, because as it stands it isn't only the maps that are slightly limited. We're also getting Ranked modes locked before we've spent time in the Regular ones.
