I think of it as a "bold" 9. Gretzky agreed it to be kinda synonymous with his favorite Howe's number 9. Yet it's 16 that Gretzky wanted at the time, instead of assigned 19...
I think all else being equal, numbers like xx, x0, and x (<10) are more desirable for perceived significance. If a player desires anything else it's presumably out of some personal significance to them (even if just 'the number I was randomly assigned on my first team').
https://www.hockeyfeed.com/nhl-news/gretzky-tells-the-real-s...