I would have to disagree with some of that. Yes, You may only be able to play 3 clans at once, but there really wouldn't be much strategy if each player could play all 5. You have to combine the clans wisely (unless your playing the single player campaign, in which they choose your starting clans for you). For example, you could have one melee clan, one ranged clan, and one effect clan, or you could have two ranged clans and a speed clan.
Also, If you could play all of your titans at once, that would be wothless, because you have to manually control each titan. And about the turrets, if you could build as many as you wanted, there would be too much defense for the limited number of goblins to break through, and if they played as a ranged clan such as hellfire (my favorite :-) ) then you would spend all of those resources for nothing, because they could take out the turrets one by one, as their range is longer then the turrets.
And although you can only play 10 goblins at a time (and one titan), this adds to the strategy of the game. You have to choose which of the 5 types of goblins under your command to put in your group of 10, which could alter the battle.