Personally, I see Mello-Roos NOT as a way around Prop 13, but rather as a way for developers to overpay landowners for raw land.
The expenses covered by Mello-Roos should be covered by the developers/builders, and should be factored into their cost basis when doing feasibility studies. They should determine the price they can pay for the land based on these costs.
We have been subsidizing landowners for far to long. End-consumers should not have to pay for the foolishness of the developers/builders. This overpayment is enabled by the lax credit market and housing subsidies.