Design so advanced that the various movie and series production teams including Roddenberry himself deliberately ignored, if not outright retconned, it until the 1990s?
Every class of hero Starfleet ships--from the TOS movies to TNG to VOY is based on what TOS created. There's no "retconning" when its deliberately designed to show an in-universe progression based on a standard, so you're ignoring how long-lasting franchises creating stories in chronological order work.
The word "seamlessly" is doing a lot of heavy lifting there![]()
Funny, the viewers who were there to see the DS9 and ENT episodes found it a seamless integration with the then-current series. I cannot recall anyone saying "it does not fit " or complained about the TOS aesthetic or production standards.
There's a reason for that.