Pay to play models that use rate for rewards are nice, but always remember, rates are random as fuck.

Look at current interest votes on it. It can easy destroy microeconomics around it if random votes lower it.

7%, 12% and 20%.

All random numbers. No math behind.

IMO without a very strict rule of changing not worth spending a single second thinking about building with it.

Rewarding a pool with 20% + trading fees would IMO also more efficient.