Have you in the same observation ? it is very hard to use White Balance or Green / Magenta Balance in Local Controls.
I would prefer a cursor working on the invert of others = near the cursor a fine tuning and far a large tuning.
Exemple : a photograph at 5200°K, a part need to be filtrated around 5000 °K. This only 200°K are very hard to do actually. Test it, you will see…
An other way could be a notched cursor gratuated from 2000 to 10000°K (or more) and a second cursor to adjust from -500 to + 500 °K around the notch selected previously.