So the only ways to get a Delta with the right nature are 1) Leading with a Synchronize Pokemon and 2) Breeding and hoping the 4% chance goes your way. Seems like a bit of a “screw you” to anyone doing a blind run, no?
If you don’t want to look up the Deltas, you’re going to make less than optimal decisions. There’s nothing anyone can do about it if you’re not going to look it up. Breeding for a different nature isn’t that bad.
There’s a guy in a house in Selene City that will tell you the nature of a Pokemon still in its egg will be. That makes it go a lot faster.
Why would you do that when you can just save, get the egg, use the egg hatcher and soft reset until you get the right nature?
Both methods take the same amount of time. They require going flying to another city (Selene or Vipik), talking to an NPC, and then soft-resetting based on the result.
The egg hatcher also lets you check IVs so even if you don’t get the right nature you can use the child to breed a better IV child so that when you get the right nature you already have good IVs.