I have owned all three 2 wts mentioned in the OP. First, to TBs point, sure a 4wt is more versatile than a 2 wt. And speaking of versatility, rod length is the biggest difference between between the three 2 wts mentioned in the OP (imperial = 6 ft, echo = 7'3", ct = 7'6"). As with line weight, rod length massively affects versatility.
For the hell of it, I once brought along a 7' 2wt along with my warm water 9' 5wt to fish on a windy lake... casting it was terrible. But I would not like casting my 9' 5 wt warm water setup on a truly tiny brookie stream with a lot of branches over it (I am not a big bow and arrow casting fan.) Or even bushwhacking with it.
So, imho 2 wts are good for small flies, small fish, small streams, and small wind. A blast in fact. I could fish a 7.5 ft 4wt on a lake, but I'd rather have the 9 ft 5wt. I could also fish that 7.5 ft 4wt on a 12 ft wide brookie stream, but I'd rather have the echo 7'3" 2 wt there. (I almost always use medium to small dry flies.)
Given the range of what we call brookie streams, the echo and ct are more versatile, because the imperial is only 6 feet. Both overline w 3t lines well. The imperial is fun on a tiny step-across stream, but not for casts of over 30'.