Annoying yes, but at least it's there. So given this option, for someone that wants their hireling to be scaled down, would lowering the difficulty and then using this console fix work to effectively nerf them?
No it won't, because HP and DPS vary according to the slider. (DPS is really damage rather than damage per second, but I'm using it for shorthand.)
If you're on master, DPS & HP (especially HP) stats are high for enemies, summons, and companions. If you're on easy, DPS & HP stats are low for all of them. You can't gimp your companion without gimping the whole game.
The console fix works to make a companion tougher (to catch up to you), not to nerf them.
Wait for mods, or don't use companions. Or maybe get a mage or somebody who's more fragile.
I've been in situations where Lydia, Joris, and Mjoll are near death, but it's rare, and usually only during boss fights, or with a large number of tough enemies.