One of my friends has a level 4 dragon yet his rank is lower than mine. When he attacks he always uses dragons.
As our rank goes up so does the toughness of enemies in war. So specialization seems to be advantageous.
The guy that only uses dragon is a lower rank than me and can attack weaker enemies. I have level 3 dragons and have to attack tougher enemies because my other troops (that I rarely used) are well leveled too.
Can anyone confirm?