It's less "do one thing with a clear intended purpose and nothing more"
More "separate the combat spells from the exploration spells and social spells."
If you want a spell that summons 10 zombies at level 3, sure. But they can't be combat zombies. If you want to push a boulder out the way, you have 10 guys to do it.
If you want a dozen bony warriors, sure. But they can't push the rock, search an area, and can't make grapples. It's Bone Sword and Bone Bow only. And they can't split up. You can make them guard a door but all of them must do it.