For me, it averages out about the same / maybe a slight benefit for T9.
Yeah, I can type faster on a modern on-screen keyboard, but by the time i go back and correct typos, fight the cursor to get it where i want it, and double check that all the words i meant to type didn’t get autocorrected into something else, I could have typed the same thing with much better precision on a T9 style and have, at most, one word to fix.
It’s something of a tortoise and hare situation. lol