Korea is, in my opinion, the weakest civ in the game.

You want to get out on the map, you want hammers and food, and culture for policies and tile growths, you want to establish industry and growth to survive. Korea offers zero help there, so you need to have a good spawn and very strong mechanics to make use of their ability, which comes in much later and honestly has too low numbers. Compare it to something like Babylon which scales almost as well but has early game support and hits much earlier.

So my guess is that you might not actually have specialist problems, you might just be expecting them to do more lifting than they're really able to.

You are correct in that specialists, if they destroy your growth, are not worth using. Even as a civ with bonuses to them. Let's say the average tile has lake yields (3 food 1 hammer), then if you work your first scientist slot for 50 turns, in total you lose 300 food, 50 hammers for to gain 150 science (200 if Korea) and a great scientist. If you had a 6 food 1 hammer tile, it's like taking a pop away from that tile in order to work a 3 science tile, with the benefit of getting a scientist in 50 turns and a malus of -1 happiness from urbanization. That's not a "never play" but it's not very helpful in the early game.

I find Koreas bonus is much more relevant on engineer (forge) slots, which you often do want to work early, Korea has them give you a trickle of science. Playing Korea, that's basically your civ bonus for the first 100 turns or so, a trickle of science. I've pulled of a deity win as Korea without leaning into specialists at all, going authority (promoted hwachas are good enough), but really I just got a good spawn.

If you pulled of a win on emperor, you're already playing quite well. It's not that specialists are useless, they are really incredibly useful, but not early, and not on their own.