Well if you think about it like this, out of all the creature types in this block the merfolk are the closest group that works along a control type of play-style. I've played literally all the creature types during the pre-release (I had enough cards for each type of deck). Merfolk felt more control, vampires and pirates more mid-ranged, and dinosaurs aggro of course. I think that if you want the go-wide strategy then you actually will need some sort of interaction with the other player. Having a strong, fast, well constructed deck is important but playing WITH the other person is just as important as playing against them.
Using blue is the best way to
outmaneuver, outclass, and outplay your opponent. Green is the best color for both growth and strength. If you want an army for your merfolks then I will strongly encourage you making the deck mid-ranged. Strong enough so that you can be aggressive towards your enemy, but crafty enough that you can still shape the flow of battle. If you had more ways to manipulate the opponent's resources then I think that this deck could also be a potentially stronger build.