Pretty sure it's just "whatever is highest" for Shillelagh between Int, Cha and Wis. Got any screenshots from your testing where as an example a Rogue has Int being used despite having a higher Cha? Your Tav for example has a 20 Int, so Int is highest.
Edit: Also FWIW any class can snag Magic Initiate: Druid and grab the Cantrip if they don't want to dip into Druid or Nature Cleric to snag it, not that it's typically the optimal feat choice but it's certainly an option.
Last edited by GiantOctopodes; 31/08/23 02:13 PM.