I have arthritis in my hands. Switching to a super soft rubber dome did more for me than any of the tons of ergonomic layouts I tried. I poured a lot of money into the problem, including getting a Kinesis Advantage. I don't think they actually have much medical benefit at all. I think everything they achieve can be achieved by just placing your hands in a more comfortable position.
My current keyboard of choice is actually a Unix layout Sun Type 7. Keys are very easy to push but not mushy.
I also suffer from rheumatism, and I spent years (and many hundreds of dollars) trying out split keyboards before finding out that my problems had nothing to do with wrist positions. I'm now typing comfortably on a rectangular chiclet (Apple Magic) keyboard.
I tried some mechanical keyboards back in the day for the "benefits". I never got it and my hands would be strained from typing on the high travel, high resistance keys. The Apple Keyboard (I use the UK/English International) is so much easier on my hands. They're easy to find, well-supported and robust.
You are not meant to bottom out on mechanical switches, you press them until the switch actuates and then stop pressing. The advantage is that if you keep pressing a little bit after it actuates, you don't hit a hard wall. The travel distance is not that much and different switches have different resistance.
Unlike the chiclet keys, where they trigger at the bottom, so you are always bottoming out and pushing against a "wall".
Everyone has different problems though. I have no problems from hurting my fingers when typing, or carpel tunnel. But I do have messed up shoulders, and having them internally rotated all day is my biggest issue.
The biggest relief for me was a fully split keyboard so that I can have my shoulders neutral rather than rotated. Other people have no problems with their shoulders.
Most of these ergonomic things do help _someone_, I wouldn't claim that they don't work just because they don't help you.
Different people have different problems. I used Apple keyboards for years and developed wrist pains. Switched to split keyboards and things got much better since then.
There are also many mechanical switches with little travel and low force (eg. Choc v1, Kailh Super Speed).
My current keyboard of choice is actually a Unix layout Sun Type 7. Keys are very easy to push but not mushy.