Surely this has been done to death? The general opinion being that you yield to the climber. I think thats generaaly crap and totally outdated personally, but take each situation on it’s own merits.
If it’s a fire road or public path where there will be walkers, one should excercise caution, but if it’s a known descent then have at it.
Ask yourself, you’re drving your missan micra up a hill. There is a broken down car in the opposite lane. Even though you have right of way, a lorry pulls out into your lane to pass it. Do you, continue on, hold your ground? You have right of way after all.
Or do you stop the car and yield to the vehicle which has much more mass to to stop avoiding a crash in which you will surely come off pretty badly.
I recently came across two (admittedly elite) xc riders climing up one of my local dh trails. A trail cleared, maintained and used almost exclusively by dh bikes. Suffice to say, I did not give them an inch. I gave them an earfull mind you.