One minor point; when it comes to physical keyboards there is functionally do difference. The JIS layout (much like the ANSI or ISO layouts used in the West) is a QWERTY keyboard. The difference is that it has kana sub legends and dedicated keys for switching from hiragana to katakana. For example, the Japanese Apple Magic Keyboard:
You’re correct that people in Japan almost exclusively use the QWERTY layout. I don’t know about your point regarding the keys being more central, unless you’re talking about the spread of commonly used keys. It’s very much a matter of it being pointless committing the kana to muscle memory when the IME works perfectly fine and you’ll be typing words in romaji often enough that it’s more convenient.