Let me ask a question about scaling and see if the point come across.
If you want to make a passenger jet that carriers 5,000 people, do you just take a 747 and make it bigger?
Yes. All planes have the same design, the inside of the plane however is designed differently for the purpose the plane is to serve.
Now do
YOU understand the point?
This is an Airbus.
This is a 747.
This is a small passenger plane.
They ALL share the exact same design, the wings are in the same place, the fins are in the same place, the engines are on the wings in the same place. The cockpit is in the same place and the shape is the same.
Federation ships are all completely different, the nacelles are in different places, the saucers are shaped differently, the secondary hulls are shaped and located differently.
Do you understand the point I am making?
The Federation only needs one type of design, they can then build that design into different sizes and design the insides of the ship to suit whatever mission the ship is to serve.
Planes can be scaled up and down and they
are. They generally all look the same regardless of size and make and model, the inside of the planes are what's wholly different.
The Federation Akira class does not need to look the way it does, it serves no purpose. Instead of the Akira design they could have simply built a bigger Nova class. The shape and design is irrelevant. So long as the new sized Nova had the same weaponry, rooms, technology and crew that the Akira has the new sized Nova could replace the Akira.