Past Tense was in season 2 of DS9. Future's End was season 3 of Voyager (kinda sucked but was decent for Voyager), TOS only had 3 seasons. Time's Arrow is the only going back in time in on earth post season 4 example I can recall.
The season 2 episode is about how it got moved up in the timeline with a pointless in-cannon explanation, I was okay with it being hand waved like the klingon ridges before they fucked that up too. I'm kinda sick if Khan and the eugenics wars being a well they keep going back to in newer trek in general, his out of universe fame has seeped into the universe. The Darth Vader effect