"Protect us all" is a completely unremarkable ability. When there are a couple of hundred Orcs, Goblins don't play any role. Assassins do. A significant one. But not Goblins. Well, yes, one dead Angel. That's it. And even then, only if they have the "Howl" ability. Otherwise, they're gone after one or two casts of "Meteor Shower," which isn't even cast directly on them, but nearby, on other creatures.

Are you still learning how to read?

The only benefit of this kind of freebie is a greater chance to disrupt the enemy's magic.
But it doesn't work well on the hero, and if you cast "Meteor Shower" on yourself and the nearby troops, it will be very bad.

Regarding leveling up, yes, Goblins are used as a living shield for Centaurs + traps.

Thanks, I laughed.
Now I understand why you need this ability – to have at least some Goblins in the final stages. And it's not surprising, because they die like flies. It's one thing to lead creeps around the map one by one, and quite another to "use them as a living shield." This is starting to sound absurd. And you don't deploy Orcs, huh?) To save resources?))
Warlords are the backbone of the mid-game army. They are tough, strong, and certainly much more suitable for protecting Centaurs.
I also chuckled about the Centaurs. You know, they can't be compared to Elves or Archers, so you won't get any "über ranged attack" from them.
That's how theory crumbles in practice.

Added 5 minutes later
A little more practice: you yourself, when you played as Orcs, did you level up filler units? Huh?
That's what I thought. I think players have long understood what filler units are.