No, they are saying the opposite. They will design the math so that 8 levels lower 5e creatures will still be threats, just easy to deal with like 4e minions of about your level.
Lemme put it this way. Minions are often built around swarm tactics. They have math simplifiers like not rolling dice for damage, so you can use many of them. They assume a basic harassment role based on their powers and abilities.
If 'minions' are made out of baseline monsters, then they lose a lot of that. You have to roll dice for their damage, slowing the game down. They don't have any nifty swarm tactics built in. They're not a strategic challenge, they're just the same goblins you fought 5 levels ago but more of them.