to be TOTALLY FAIR, at that point, TNG hadnt come into its own, episodes like code of honor, , angel 1, etc, with badly written scripts, and cheesy special effects, predominated.
So I can understand why at the time they may may have found it safter to give it a place in a Feature lengh movie I just mourn what could have been, Khan's descendents, ariising...
I think you're misremembering the timing. The Wrath of Khan
came out in June 1982. The Next Generation
did not begin to be developed until October 1986 and didn't premiere until a year later. So it's not like it was a choice between one and the other.
What could the augments have done in between creating simplistic spaceships, equilivent to mercury and gemini, and and viable interstellar travel, since its going to be years and lot of focus on vengeance...
But would there have been any reason for vengeance? If we're assuming Khan's people survived into the 24th century and that the promise hinted at in "Space Seed" was fulfilled, then we're assuming Ceti Alpha VI never exploded, that they were able to build a civilization on Ceti Alpha V. They might still have seen themselves as potential galactic conquerors, the naturally superior rulers, but what's their motive for vengeance?