After many edits, I found the last one to work...
Its level. Change it to level 100. That's it, nothing more. I thought there was more. Changed ball, memories, rerolled PID/EC, added level 1 moves Tackle/Dragon Rage, friendship level, no PP Maxing out. Even built a Hydreigon from scratch using your info. The only edit that worked, was changing its level. I tested out a level 50 Jirachi to see if the 50 minimum was taken out, it got through. So I don't know, it could be Draco Meteor being taught to level 50 pokemon?