"Many racers only do tacks in this wind, for the same reason."
-> I feel exactly the opposite, the wind will become so low that im not able to tack anymore (if i do i wont have enough exit speed, ill touch down, sink and drop my kite), but i still can jibe (barely, but not touching down). Ive heard some guys saying that if they can jibe they can also tack, but also others saying that if the winds get under a certain point they will jibe even at the upwind mark to not risk dropping their kite in a tack.
For me no way i can tack in race gear under 5-6 knots, but i still can jibe in those winds, and keep going in 4 knots. Still need to pratice ALOT in this winds, this is where good racers really impress me, the ability of keeping the speed and nailing maneuvers in very light winds.