I managed to breed a 6IV Gengar, 2 6IV Growlithes, and a 6IV Eevee. Luck is extreme in me!I breed 90% of my pokemon. 9% are events. 1% are inserted pokemon that I use for breeding partners. The only inserted pokemon I use is my 5 IV Event Gengar and I inserted it because I was going to reset until I got one anyways. I just wanted to save time and aggravation. Besides, I'm of the opinion that it's less about the IVs of the pokemon and more about how one uses them.
After all, a Pachirisu won last year's Worlds. And it won because the person was very strategic in how it was used.