You shouldn't be looking for the “right” names for your progression tiers. The ones that fit your world perfectly and really click for you.
The truth is, literally anything works.
You don’t need to look for the terms that fit your world now, just pick names you like and then change your world to make them fit.
Cradle has Copper through Gold for the first advancement levels, but precious materials have absolutely nothing to do with the sacred arts. That was just an easy way for me to visually show progression, so I picked valuable materials and then changed the setting to support that choice.
You can pick any labeled sequence. Materials that increase in value or hardness. Luminosity; maybe someone starting out is Dull and a master is Radiant (or a Windrunner ayooo). Someone mentioned colors, which would absolutely work because a rainbow is a labeled sequence.
You could still DO colors that don’t progress in order of the rainbow, but it’s less intuitive.
There’s increasing physical scope: he’s a room-scale mage because his spells can only affect anything in the same room he’s in, but this archmage over here is a national-scale mage who’s shaping the weather and sending his eye familiars all over the sky to watch you.
Increasing size: Tiny, Medium, Large, Massive. Sounds stupid? Sure it does, so tweak it: “His brontosaurus shook the earth with its steps, so its body contained enough mana to bury their entire camp. She hid inside the doorway, closing her eyes, clutching her shivering baby velociraptor to her chest.”
In that case, you don’t need official categories. Big, Bigger, Biggest. You just need to know that the bigger your dinosaur is physically, the more magic power it can hold.
In that way, a progression system doesn’t need discrete tiers. If your magic capacity is measured in balloons, and you have fifteen balloons of magic but the enemy has figured out how to get one massive hot air balloon, who has the advantage? How does that affect what spells you can both cast?
That’s something where the comparison isn’t as clear-cut as it is in Cradle (a Jade beats an Iron every time), but there are still crystal-clear methods of progress (increase the size of your balloons or the number).
I say all this not to give you more ideas, but to encourage you to stop spending time trying to think of the one that fits your setting BEST. Any of them work.
The one that fits your setting best is the one that you make fit your setting. So spend an hour brainstorming, pick the idea you think sounds the coolest, then work it into your setting.
If you finish your first book and your readers tell you that your tiers of progression are dumb (which I can’t imagine unless they’re intentionally ridiculous, like you measure power output in Spirit Clowns), THEN you go back and change it. It’s no big deal to change it later.
Any tips on how to overcome this hump?
Yes, pick literally any progressive sequence, attach it to your setting, and move on.