National unions do not negotiate salaries at the national level. Salary negotiations are done at the local level from district to district done by local union reps.
Not all negotiations are about pay and benefits. Presumably there is some benefit in being organized at the state and national levels or unions wouldn't bother to do so.
Definitely there are reasons for having a national union. But you made a statement about not abdicating negotiation power to national unions. I assumed that by this you meant salary since that is the subject of the article about which all these discussions come from. Of course, things do get off topic and so I'm sorry if my assumption was incorrect.