I choose the Arca system for several reasons, one being control of focus.
True if you have a CMOS back, focus can be controlled very easily via Live View as Guy's Credo 50 review showed.
I also learned early on, that the wider lenses, 28, 35 and 40 have such a great hyperfocal range, especially with a bit of tilt, that you can map out the hyperfocal range and in many cases use that. At least it works very well for me.
As you move longer, exacting focus is much more demanding and you DOF gets even smaller.
I personally love the Arca card which gives you a great starting point, once you have measured in your distance. This is very critical with the 60, 90 and especially the 120 APO. You can then fine tune the focus, and if you shoot tethered, this is so much easier.
Many seem to feel the Arca solution is too "tech", and it's a very personal thing for sure. For me, it's a huge time saver, and get the job done. I have great confidence when moving to the longer glass, which is where you seem to want to start.
Cambo and Alpa can use the detailed focus rings on the lenses, which can also help to fine tune your focus.
Quickly back to your lenses:
The 90 HR Rodenstock, has a 120mm or 125mm image circle, and is a fine optic. It will ghost flare at times and this can totally ruin the shot. The Ghosting can come with a hood and the sun at your back. You just have to watch for it and try to find an angle/hood combination that prevents it. The lens is a nice size and weight and easy to carry in the field. I have an older HR and it's a bit softer on full shifts on a full frame 60MP back.
The 120 APO, is an excellent optic, again with a huge IC. This lens easily will shift to 30mm on my rig, (when I rotate it so rise fall are shift). It will focus pretty close also, in around 6 feet. As it's a Schneider, the ghosting flare is not an issue and it actually does very well when shot at the sun, as all the Schneiders seem to do. Great lens, tiny in size and weight.
Paul