The U.S.S. Enterprise-Original went through some REAL cosmetic and internal changes from the time of April-Pike and Pike-Kirk and from the first year of Kirk's 5-year mission and the 3rd year of his mission did it not?
Where in TNG do you find a ship that can travel easily 30,000 ly in less than a few weeks?
Where in TNG do you find a ship with psycho-tricorders able to read the memories of a person 24 hours after the events?
Where in TNG do you find a computer that can tell if a person is lying or a computer that can beam a person back into themselves or even one that travels in time to investigate the past on a fairly regular basis?
Where in TNG do you find a ship that can travel a few thousand light years in less than a day?
The Next Generation doesn't come close to this-exception counselor Troi. Now are you going to include this in the manual?
One thing I noted was the differences in engines-the old ones had no Balls on them and I think it was a modification of those engines to include the balls as a safety regulator so Kirk and crew WOULDN'T get into so much trouble so far from home.