LiveView helps by magnifying the image enough that you see exactly what the sensor sees. It certainly doesn't help reduce the apparent vibrations .
Your Manfrotto 475B has a 35mm upper leg diameter. That is slightly less than a Gitzo Series 4. A Series 4 alloy would probably slightly outperform your Manfrotto, or it should, considering it cost twice as much at the time.
My CF Gitzo Series 3 very slightly outperforms my alloy Series 4. That suggests a Gitzo Series 3 will improve things a bit but it won't make it easy.
If you really want to solve this problem, try a Gitzo Series 5. If they made a Series 6 or 7 I would suggest that . Just to say it's a tough problem that is only totally solved with a concrete pier with a 3 foot long concrete encased footer embedded in the ground.
I think there is some confusion here. Your stated problem is not getting a vibration-free shot, but simply how to manually focus a rapidly vibrating target. Hopefully I got that right . How to get a sharp shot is a totally different matter (and maybe no easier to solve).
Since no tripod can totally solve this problem, mostly I think it is a matter of skill and daring, and learning how to focus a moving target. I use long lens technique, and try to focus with a light touch. Which is difficult with my 500/4 because the focus collar is very stiff.
I would be surprised if your gimbal is actually stiffer and more vibration free than the Markins heads. Gimbals make it easier to frame and track targets, but they aren't truly designed to be more stable- they can't be because they are relatively too complicated in terms of the mechanical physics.
I have never seriously used a beanbag because they create some practical problems. One of those problems is that they tend to interfere with the focus collar. When manually focusing I'm not sure where to put a bean bag that makes sense.