A few people in this thread have commented about how we all have a tendency to judge what we're currently used to as the ideal just because we're used to it. Most of us are pretty emotionally biased in this way.
I was too until I sought to justify my former obsession with mechanical keyboards by doing a series of typing tests to measure how much better I could type on my favorite board vs the worst one in my posession. The results surprised me. I took 5 minute typing tests on each. There was barely a difference between my favorite board and the most garbage keyboard with stiffened rubber domes.
This isn't to say that every keyboard is fine for anyone and they just need to learn how to use it better, but we shouldn't make definitive judgements based on short exposures. Some people are much better athletes than others and have an easier time adapting their movements to new situations. Some people are better artists. Some can analyze tones or compose music better. Besides having different physical strengths and limitations, we each also have differing cognitive abilities to adapt to our environments.
I'd like to see a similar test, but where the metric isn't typing speed, but comfort?
Keep typing on each, until you have to tap out. Until you're, "screw this I'm done with this one".
That would be more useful data than typing speed for most everyone, outside of people doing data entry professionally, I'd think?
Someone who's a proficient typist more than likely can grind out WPM for 5 min fairly consistently across input devices, as long as the starting hand/finger positions are all relatively close?
Long-term comfort, however is going to factor in several ergonomic factors, including key travel, hand position, etc...