... that is literally what they're doing with this change? while minimizing the devaluation of accessing preferred seats for premier members (which maybe not relevant to majority of people here since they usually get E+, but premier members do enjoy having the benefit of being able to select seats further forward in the cabin as opposed to row 39).

But this change is literally resolving the point you're saying they need to get rid of. If no non-preferred seats are available then the seat map will release adjacent preferred zone seats for no charge for purposes of allocating an adjacent seat.