My shinie legends are my Thundurus, Genesect, and Darkrai.
All 6IV, 99.999% likely to be hacked
I've actually seen more Shiny Genesect from Shiny collecting Passerbys than normal ones. And I've only seen *two* people with Shaymin and ZERO Manaphy traders. That said, I'm pretty sure your Genesect is real.
Plenty, plenty more of Phione traders, though. Those guys are the first thing Passerby seem to reach for when they attempt to show interest in my shinies. Phione is one of my least favorite pokemon...But I adore Manaphy.
If they dont have Shinies, many Passerbys I run into flash more Phione, Zoroark and Druddigon than I can count. ESPECIALLY blasted Zoroark...
My Genesect is 100% hacked. It's the event shiny one, which has set IVs. Only two of the IVs are perfect. Mine has all six.
By this logic, no bred pokemon should have moar than 3ivs (5 with DN), and your Xerneas/Yveltal never have more than 3 either..
You are assuming that Event Distribution is a perpetuity, which it isn't, unlike breeding. You can breed as many pokes as you'd like. There were only so many of those genesect given out.