Glad to explain, Suijin. I think you were starting to get to it with the edit at the bottom of your post.
Let me start with looking at the forces when hand steering. In order to turn the wheel shaft, a torque (purely rotational force) needs to be applied. To accomplish this, the helmsman places a hand on the wheel rim and turns it. When turning the wheel from a single
point on the rim, a torque is applied to the wheel shaft, but there is also a linear force being applied to the shaft. This force is parallel to the tangent line of the rim where the force is being applied. So, if the helmsman's hand is at the top of the wheel and they are turning right, the force that they are applying to turn the wheel is also a being applied to the wheel shaft to the right (this force is equivalent to them just pushing the wheel shaft to the right, without the wheel being there). Now, if the helmsman has two hands on the wheel, the torque being applied is shared between their hands, but there are two separate linear forces also being applied perpendicular to the wheel shaft (say, on slightly down and to the right and another just to the right). This force places additional load onto the wheel shaft bearings - and mostly the aft bearing (There is also another moment load the bearings must handle that is related to the length of the exposed shaft, but that is significantly less in most cases and we'll ignore it for the purposes of this discussion). Now, when hand steering, the skippers hands are never in the same postion, they will move depending upon if they are sitting or standing, or even if they just want to shift their arms. So, the wear that is caused by this additional force is spread out considerably around the bearing housing - this means a slower and more uniform wear all the way around the bearing housing.
Note that there is also loading on the wheel shaft from the chain, but this is distributed evenly across both bearings. This means less wear, since it is distributed over a larger surface area, just like the double aft bearings do on the 400 series Edson
pedestal for wheel loads.
Now, in moving to windvane
steering. As Suijin mentioned, the lead into the wheel is fixed, so the lateral loads are always in the same direction. This means that the bearing housing will be worn more in one direction than another. To further aggregate this issue, the wheel adapter for the windvane is smaller in diameter than the steering wheel, so a larger force must be applied to turn the wheel. This also means larger linear forces, so even more wear. Again, a double bearing and stainless bearing liners attempt to mitigate this problem (as in the 400 series pedestal).
I hope that addresses your questions, but let me know if you need further clarification anywhere. I know some of this was written a little heavy in engineering lingo. Given you have a YS pedestal, it is possible the wear is only in the shaft bushings. They did not use needle bearings, just bushings, to the best of my knowledge. So, if the bearing housing is still in good shape, new bushings may tighten it all right up - the only problem is trying to source these. It may or may not be worth it... in most cases it is the latter. You will have to take a close look to see where the wear is located.