That's definitely a good Diancie! Congratulations on getting it. I tried to soft-reset a competitive Hope Diancie as well, and ended up coming across a Brave one with 0 IVs in Speed, 4 perfect IVs, and one "not perfect" IV. I didn't think I'd get that lucky again, so I saved the game after that! The combination of a good nature + a fortuitous 0 IV + a decent IV spread convinced me it was the "right" Pokemon to hold onto.