As an experiment in discussion (not necessary how the game should be changed) I love your initial idea. It actually reminds me of CC in Pokemon - where most of it is "soft" and has penalties with only one "hard" CC - which in Pokemon is Frozen.
My main suggestion to this would be to allow some additional hard CC, given the soft debuffs that already exists (chilled, wet, warm) - but most hard CC would require a progression to actually apply. This actually was more of a thing in DOS 1 due to the % change to apply CC (much easier to freeze if they are wet or chilled).
- Stun would require Wet (or maybe add a "shocked" soft state from Aero)
- Freeze would require Wet or Chilled
- Petrified remains as is possibly (unless a new "oiled" is required, which could also combo with fire single damage spike)
This way hard CC is possible, but takes more setup and strategy than it does today in DOS 2. Hard CC is spread across Aero, Hydro, and (lesser extent) Geo. Obviously spells will have to be balanced for this, so some things can only apply Chilled but never frozen (or only apply Frozen if combo of chilled + wet from Hydro).
