For the past decade or so, I have been trying to do the same thing with on-screen keyboards (tablets, phones). It's been a total failure - and I'm quite annoyed by my lack of progress with those. No matter what I try - pecking the screen with my indexes, trying to use my thumbs (seriously? how do people do it? thumbs are the largest fingers, how do you hit the letter you want with them?), using a wavy movement with my index, without lifting it until the desired word is suggested - everything I've tried is far less efficient than typing on a keyboard, even on a lousy one.
What am I missing? How did you get proficient with on-screen keyboards, fellow HNers?
But: every time I use an iPhone (even an iPhone 6) my "precision" is much better - not sure why. Its even more pleasurable and tactile.
(I remember back in the day people said that "iPhones had a faster display update" - maybe that is still true?)
I noticed a substantial improvement when using Colemak, perhaps this is where QWERTY really falls apart.
Typing on a screen it's harder because you can't touch typing (since you don't have any home row bumps); you must gaze at your keys, therefore your eyes HAS to move back and forward between the keys and the whatever text you type.