Surprised people aren't suggesting mixed opposition. Monsters with a high CR tank pinning down paladins and fighters, low CR but nimble skirmishers attacking squishies and monster archers or casters peppering the party with missile and spellfire.
Then the monsters tend to be easier to align to the PCs.. just like on the battlefield of the Ancients..
Then the monsters tend to be easier to align to the PCs.. just like on the battlefield of the Ancients..