Unions are what their members make them, The officers are elected, and it is certainly not hard to get elected shop steward in any union I have ever belonged to, which include the NEA, the AFL-CIO and the UTD.
Union members make about 15 to 20% more than non union workers in the same jobs.
There are companies where the management treats for workers decently and no union is needed. But not many. Teachers without unions get screwed.