Re: TOS and purely comedic episodes
Since those comedic episodes all came in the second season of TOS, maybe Roddenberry & Co. tried to reach a broader audience with that approach. They constantly struggled to keep the show on the air, so they may have even been "urged" in that direction by studio/network officials. Just a possibility of course, that I´m sure someone here can confirm or deny.
"Do you give me attitude, Spock?" - "I´m expressing multiple attitudes simultaneously, Sir. To which are you referring?"