I don't understand. Why not put the lens directly on the monopod head versus off to one side?
For a gimbal to work the lens/camera needs to rotate freely in the horizontal and vertical ranges while being well balanced so it stays in place when you let it go.
Of course you can't let a monopod go.
You can get horizontal motion by simply turning the monopod but vertical motion is problematic if the lens is firmly attached to the monopod.
Gimbal heads can have horizontal and vertical orientation. Ones with a vertical orientation that center the lens over the center of the pod tend to be heavy.
The Wimberly monogimbal head is a compact side mount head. Of necessity the lens is offset to the side of the head, that is the only way it can be so compact.
I have one of those. It is not a big deal to tilt the monopod slightly to the side to balance everything.
Using a monopod makes it easier to transport and use a heavy lens. With practice the monopod head works well as a gimbal but it has drawbacks compared to a standard gimbal head on a tripod.
A well-balanced gimbal head on a tripod makes handling a long lens smooth and easy. You can point the lens just about anywhere and when you let it go it stays there. If you have to wait for something to happen you can just wait, you don't have to hold on or tighten anything down.
By contrast a monopod is inherently unstable. You have to keep your hands on it and it is very difficult to avoid camera shake or motion.