This is what I used to get 100:
This was the first week of the league, so there's probably even better strats now, but I know a lot of people pushing to 100 recently that more or less did exactly this. I also think subbing in a delirium scarab over a domination shrine is good as more mobs = more exp if you've got the build for it. If you're a mageblood minion pacter you can go even nuttier and delirium your maps with deli orbs and crank some other scarabs and leave the Domination scarabs out. With Breach I would 100% absolutely do Dunes over something like City Square. If you really wanna min/max you can use full Mirage maps. I personally didn't fuck with 16.5's because of some of the dumber mods like Tentacles. I also didn't roll for pack size I just regex'd for safety and blasted for 2-4% per map at 99.