Actually it does make sense, especially for capitals. Ships are deployed in divisions, and the closer the characteristics of the ships in a division, the easier it is to use the division. What better than several ships of the same class?
5th battle squadron
USN standard type battleships
The IJN tended to group ships of a class together, from heavy cruisers up.
Most destroyer flotilla's were composed of ships of the same class.
The idea of designing several classes of 1 type would be good for custom battles, but not having that ability isn't that weird.