Just wondering =)
I didn't include EVs cause there is a question for that !
All Pokemon do have a nature, however this is the only unique thing about the gym leaders' Pokemon, they can't have their hidden abilities, and they don't have IVs
Hope this helps
A few galar gym leaders have hidden abilities, Melony's Darmanitan has zen mode, piers' scrafty has intimidate, Nessa's Drednaw has swift swim, etc. I haven't checked all of the gym leaders but yeah, some have hidden abilities