Showing them as states sounds good. If you want them to stack then you may have to find a way to implement that (YEP Buffs & States Core?). Alternatively you could make 8 "dummy" states (1 per basic parameter) and add a State Rate trait wherever there is a corresponding Debuff Rate trait. Then the states could be used to show "debuff rate" and the debuffs would still work like usual.
Otherwise, I happen to have an add-on for YEP Status Menu Core that lets you define custom values for its Attributes list. Plugin link:
For the Value formula, this may work (untested):
JavaScript:
this._actor.debuffRate(0)
Replace 0 with the parameter ID:
0 MHP | 1 MMP
2 ATK | 3 DEF
4 MAT | 5 MDF
6 AGI | 7 LUK
If you want resistance instead of rate, try
1 - this._actor.debuffRate(0)
instead.
There may be other options~