Today I Learned

It wasn't a matter of typing too fast that was the issue, but rather commonly paired letters should be positioned such that their mechanical linkages would be less prone to collide with each other if they were pressed consecutively. Your only real limitation in typing speed on an oldschool mechanical typewriter is that you can't have two keys pressed at the same time and you can't have two hammers hit the page consecutively before the first hammer has fallen away. Commonly paired letters should be mechanically unlikely to collide, which does not necessarily follow that they wind up with an intuitive location on the keyboard itself in terms of what's "far apart" and "close together."

On the Sholes and Glidden typing machine from which the modern QWERTY layout was originally derived, the hammers did not have a return spring but were rather dropped back home via gravity. Later models quickly developed spring loaded returns for just that reason.

The Sholes and Glidden 'board was tweaked somewhat from its original quasi-mathematically determined collision mitigating layout largely for marketing purposes, and also for aesthetics. The primordial design actually had the period key in the middle of the field which probably looked just as goofy to people back in the day as it does now. The rights were eventually sold to Remington (yes, that Remington) who made the final adjustments to arrange the keys in the modern QWERTY layout, invented the shift key for both upper and lowercase letter capability for their Model 2 Standard typewriter which the Sholes and Glidden machine lacked, and the rest is history.

I'm pretty sure QWERTY telegraph keyboards post-date typewriters. Early examples of telegraph transcription machines literally used piano keyboards with letters inscribed on them, and the prototype Sholes and Glidden 'board inherited a similar two row layout before adopting the staggered four row one.