The pay scales of public employees might be decided by an impartial referee committee that has no vested interest but the public interest (as much as is humanly possible).
Politicians should not be directly involved in negotiating with unions.
I believe in the very high value of unions. However, it is true that most people make decisions on the basis of personal interest so that strong unions exert an undue influence on pols.
I tend to be a little nervous about handing something inherently political over to a committee that would have no accountability.