Gotta agree, an XXL stem on a too short frame is bad... But in this case, much like mine, he is already on a XXL frame.
I resisted the idea of going to a XXL stem forever..Seemed wrong to me. But one day, Harry Leary tells me to put on a longer stem. I protest.. He says try it... If it does't work, take it off. 3 laps later, it felt great, haven't changed since. Even when I stepped up to a XXL frame, I left the stem alone. Makes my 20 feel more like my cruiser. I love having the room to move around.
Same with the spacers under the stem... I set both bikes so the bars were at the same height... Didn't account fo the difference in BB height... Take a couple of measurements, change some spacers, total change in my riding...