My strategy was simple:
For every low, medium, and high threats (including three birds, also epic boss) I would buff Thor with protect, gamma booster, and revenge strike. Thor would get attacked by the opposing enemy thus buffing Thor with 2x enraged, 3x gamma buff, plus he'll have 2x MoM. This cause maximum damage resulting in ONE SHOTS AND EPIC OVERKILLS! Useing Summon Thunder did wonders!
My agent and Dr. Strange played the supporting role healing Thor and themselves so I can get 500 vitality points. I would also get the quarter master bonus as well. This is very doable in 8.5. Please don't report because no one cheated to get this scored. I just earned the highest points possible by creating the best strategy. Now if you see someone with a score of 4,589,000+ then that's something fishy (like the guy ranked #1 in my screen shot).
I read your post about the guy who has a score of 700k+. This score is possible. I myself have scored 730,000+ easily. Here's my proof:
I did not cheat in anyway type of form. My set-up was:
Dr. Strange (the old Dr. Strange, the one who never had passives of an update)
Avengers Blaster Thor (Again, the old Thor, when his inspire bravery had a cool-down)
Equipment for Agent: