Originally Posted by
headset
I was three days into 10 tour and REALLY needed to raise my bars 1.5 cm - took 30 seconds with a quill stem. Another rider using threadless stem was also struggling with a handle bar height issue - and he suffered the full tour because of it.
Not sure how functionally superior that is

That's more of a cut steerer problem than a threadless stem problem.
Some people don't like the look of spacers above stem, either, though. That's just an aesthetics problem.
Of course the threadless adjustment would still take a bit more than quill adjustment. Perhaps 90 seconds instead of 30.
Now if the two of you had needed stems with different reaches then he'd be much better off.