Actually, you don't really need tiers that much...
Just only need 3 ways(4 for some) to classify them:
Easy to use mode
High risk, High reward mode (also called Hard mode)
Trash. (Lunatic mode, very few units end up here.)
Unfortunately, lots of SDGO players nowadays forget about Hard mode, which is why people are spamming Brainless mode.
Dame da, Zen zen dame da ze.
No good, completely no good!
Now, repeat it in red!