Very few people thought that typing on a touchscreen smartphone would be a good idea. It was commonly thought that without physical buttons to press, it would be too cumbersome to type correctly. With no keypad there would be no guidelines when trying to press the correct button, and no feedback to know when a button has been pushed.
Several years down the line, that school of thought has been proven very wrong. Touchscreens have been a great success. With no physical keys to get in the way and without the need to actually fully click down a real button, touchscreens are even easier to type on. Add in the introduction of auto-correction and swiping, and typing accuracy is as good as ever. The typing speed of the average phone user has surely increased.
On a screen that can comfortably fit two thumbs and the space for them to move around, there is no problem.
Input on Smartwatches, on the other hand, is not quite as ideal.