I've found that Sab can be useful without TR and KC if you have a deck that will reliably draw itself every turn. But ONLY then.
I've had a few good games with sab recently. One was a colony game with university and rabble. I went for university, used the universities to gain rabbles. My opponent skipped university, and so got off to a much quicker start; I think he had two colonies and two plats by the time I got my first plat. But at that point, I was cycling through my deck really fast, and gaining multiple 5-cost actions every turn for free; most of them were rabbles, but I occasionally made them sabs. Had two by the end? Maybe three? (I think there was also some other village around? Which I also gained with universities sometimes? Don't remember) I ended up winning that game something like 4 colonies and a province to 1 colony and 4 provinces, having rabbled his colonies to the top of the deck and then sabbed them.
There was another game, also a colony game I believe, where there was a city race which I lost. My opponent then added in some more money and started greening; I kept trashing (with, I think, Masq?) until I could draw my whole deck, and then added in a sab and a late-game sea hag, both of which which I played every turn, and ended up pulling out a win.
Also had an IRL game where I went for a native village//library engine, and added in one late sab. (In retrospect, that one was a mistake which I got away with rather than a good move, though.)
I think the excessive draw power and excessive free actions are key here. Sab takes up a card in your hand, and it costs a turn to buy it, and it gives you no benefit. So that really sucks. However, if you're drawing everything in your deck anyway (or, at least, drawing lots of cards, if not your whole deck), and are doing it reliably, then the one card slot doesn't matter. In all three of those games, I never felt like I wished I had drawn [something else] instead of the sab, because I drew everything I wanted already.
And if for whatever reason, you have an excess of actions, then the fact that it's a terminal action doesn't matter. In all three games I'm remembering, there was a reason to overinvest in villages; in the uni case, my 'village' was also a gainer, in the city case my village was also my card draw. In the NV/Library case, NV contributes pretty well to the card draw, since library draws up to 7 anyway AND then you play a single NV to draw up all the cards from the mat. And with early steward trashing, I had lots of $2 turns anyway.
Of course, Sab still has the opportunity cost of buying it instead of another $5. So you're giving up one turn of purchasing power advancement in exchange for hurting your opponent by $2 per turn. I think it's sometimes worth it.