I think Shere Khan is worth the “risk”. Even if there is some overlap with Snow White characters, your likely to get their items since his items are legendary. Might as well try getting an extra fire stick or hat before the Snow White event begins.
I’ve got about 13 hours left on my max leveling of Cheshire Cat. I should be able to max level my Alice, 1 hat short, when that gets completed. My level 7 Queen is at 15/24 and 11/24, so even if I can get her ready to level before the Snow White event begins, I think I’ll wait.