Two tier compensation systems never work well in the long run.
They create a “them vs us” environment and generate resentment.
The lower, lesser compensated tier eventually works out ways to balance the scales - at least in their own minds.
They decide “if we are worth less, then we will give less and will take more when we get the chance.”
I knew a government employee who once told me “They pretend to pay us, and we pretend to work.”