Having come from medium format and 35mm, without the advantage of movements, I always wondered about landscape horizons that never seem to look flat.
I think that's mostly about not having or not using the available tools to ensure the camera back is vertical and parallel with the face you don't want converging. With 35mm and most medium format, you have to tilt and rotate the camera to frame (not even shifts and rise, never mind swings and tilts). Guaranteed to get stuff off kilter.
You just made me feel better. I just started with LF when Covid started and don't like the upside either. So I got an eye-level reflex viewfinder (as I got one for my medium format waist level camera with left to right reversals). OF course, it works very well with my 300mm lens on my 4x5. But it's harder to see with 90mm and 75mm. Any suggestions in getting the images to look right when they're harder to see?
My recommendation would be to spend enough time under the dark cloth to retrain your brain.
When I was in high school (back when a Camaro had a big V-8 under the hood and a Toyota pickup didn't) there was a drawing exercise: to draw from an existing picture (drawing or photo) mounted
upside down -- many who had trouble drawing a likeness found it far easier with the subject inverted, because it let their brain disconnect from drawing what it
knew was there and draw what it
saw. When I started large format (with a plate camera in 2003), it took me a little bit to learn to "see" the inverted image -- but not long. I suspect it was because I was already trained for similar stuff; I used to have fun in grade school, standing in front of another student's desk and reading the same book they were, upside down, and I could also read in a mirror almost as fast as I could the regular way.
Regardless, however, it'll come with time under the dark cloth.
As for making the image more visible with the reflex viewer and shorter lenses, I'd suggest a Fresnel overlay for the ground glass. This generally brightens the view anyway, and it'll correct the continued divergence of the rays from the shorter lenses.