One missed opportunity in TOS is the Earth Romulan War and why Lt. Stiles is still so angry after 100 years. It would be like Americans in 1912 still bitterly hating the British over the War of 1812.
So an episode about the Earth Romulan War would've been nice, it could've gone like this:
Uhura: Captain, why is Lt. Stiles such an angry man?
Kirk: Well, its like this lieutenant--- "fade to flashback.
An FTL Earth ship comes across a huge armada of what is later known as Romulan warships which are not FTL capable. It hails the nearest one and in reply, the Romulan ship simply fires an atomic weapon. The FTL capable Earth ship easily dodges the bomb moving at sublight speed and determines the huge Romulan fleet will reach Earth in 57 years.
After 24 years, having built a fleet of 80 FTL starships and having gotten tired of waiting, the Earth fleet goes out to battle the huge Romulan fleet
Well, saying it was like shooting fish in a barrel vastly understates how easy it was for the FTL Earth ships to destroy the sublight Romulans ships.
The Romulans didn't have a chance, they couldn't even SEE the damned Earth ships.
In fact, the crews of the Earth ships got so bored, they came up with a game of seeing how many Romulans ships a single Earth ship could destroy in a single pass at maximum warp speed.
So it came down to the record was 59 Romulan ships destroyed in a single pass and there were only 60 Romulan ships left.
So one Earth ship captain went for a record but having killed 59 Rom ships, this captain manages to run smack into the very last Rom ship, destroying both it and his own ship.
It came so close to being the perfect war for Earth with 100 percent Romulan casualties and 0 percent Earth casualties but thanks to this idiotic captain at the very last second, it didn't happen.
Captain Dunsel Stiles would go down in history as the worst, most useless starship captain ever by far.
Uhura: Oooh woow, no wonder Lt. Stiles is such an angry man.
Kirk: Yep.
Robert