I got my 7th legendary off a mythic dungeon boss last week. I've done probably over 300 regular mythic bosses.

Two characters have 2 the rest have 1.

3/4 of my DKs have sephuz's secret. I guess with its incoming buff in 7.1.5 where it activates on interrupts that it will be less awful. At least I can easily proc it on trash but its useless on most dungeon fights since I'm unable to proc it.

Legendary Sources:

2 were from mythic+

4 were from emissary caches

1 was from regular mythic.

I do like the +15 legendary ilevel bump to 910. My toons are now all around 870 ilevel.