Well, I have been working on this since 5e came out, so I get it!
That is why I started with making epic monsters first!
5e Epic Monster Updates But those are just first drafts (200+ of them though). They will all have to be updated to my new system.
The real problem to me is what are high level mooks? I think I have basically decided that hordes, legions, host of demons/devils/angels are the new mooks. Of course, ideally when your playing deities, you can find other things to do than fight. I am working on that front too.
I have decided to make the players & monsters abilities and stats relative based on their epic rank. So, if you look at Athena's stat block, epic rank 4 (greater god), her stats are for use against other creatures of epic rank 4. However, if she engages a creature of a different epic rank, her stats are modified.
EX: Athena's spear attack does 50 damage against an Epic Rank 4 Titan. that same attack does 800 damage to a mortal creature (Epic Rank 0). Hit Points are similarly relative (she has 1500 HP vs ER 4 & 12,000 HP + resistance to all damage vs a mortal).
I debated whether or not this would be too complex in play, but I think I have done most of the work in the statblocks themselves and it leads to such interesting interactions I think I am going to stick with it.