The majority of ships aren't SI ships. I however, do find the number that are funny. There are a lot of sovereign class ships and I don't think it is because there are a lot of ships available. I don't buy that.
People use it because it is the flyest ship in the fleet.
I wouldn't call it a creative rut, justa trend. DS9 has all these intriuge stuff going on, and that will influence the sims. The Sovereign is a sweet ship, so it will be popular. But I do think that the common adventures of a starship need to be focused on more. The trend is for galactic conspiracies and epic battles.