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".
I've often thought this as well. I first noticed it in TWOK (Weapons were not used on other ships in TMP). Phasers and Photon Torpedoes seemed super weak when compared to TOS levels. Even against unshielded ships.
I've discussed this on other forums and others pointed out to me that it probably wasn't that the weapons were weaker, but the ships, shields, SIF and the hulls were much stronger on the newer ships and could take more punishment. I like this explanation much better and it makes more sense logically.