Can you hold one orientation over a marker? For many years, I could hold a stationary hover in all upright orientations, and slowly pirouette, both directions, - just not over a marker. I was letting the heli pick the spot it would stop over.
I recently (last year) decided I needed to learn to hold the heli over a spot. The problem is that trying to hold the heli over a spot splits your concentration and focus as you need to be aware of where the spot is and also to keep the heli still. Then if you are not over the spot, you need to move the heli back over the spot.
This requires reflexes to know precisely how much to move the stick, and in the correct direction, to bring the heli back over the spot. It goes something like: move the stick a little in the direction you want to go, the heli starts moving in that direction, once you get close, stop the movement by giving a little of the opposite command. If you gave too much opposite command, it starts going in the other direction so try again with less movement. It's like learning to hover all over again.
Once you can hold a stationary hover in all orientations over a spot (tail in, nose in, nose right, nose left, then 45 degree variations), the slow pirouette will actually be easier than holding the stationary hover, because the heli will rotate through your weaker orientations and soon get to a more comfortable orientation.
Sadly, I don't think there is a secret that F3C World Champions are holding from us. It is all about visually noticing the heli drifting, in what direction, giving the precise correction to stop it, bring it back, and stop it again over the marker. Then keep repeating with small inputs as quickly as you notice the movement. So basically I think you have to practice enough so that the corrections become a reflex.
As others have said, this type of flying must look very boring to onlookers, but I personally find it very rewarding, and I have great satisfaction when I can hold the heli motionless over a spot. Welcome to precision helicopter flying.