I never got the sense that nuKhan contributed to the technology per se
, but more that his "savagery" allowed him to think of concepts and tactics that the more pacifistic 23rd century humans would never even consider.
Back to the topic of the thread... the different iterations of Trek have always been inconsistent. Based on on-screen evidence, the original TOS Enterprise seems substantially more powerful than the ships from the TNG-era or JJ-era. It only took a couple of phaser shots to kill everyone on Excalibur in "The Ultimate Computer" or completely obliterate a Klingon cruiser in "Day of the Dove".