Am I right in thinking this arrangement maximally benefits the employer and tends towards a single union situation?

When a union fails to represent its members, they should form another union. If they do so, they will be forced to renegotiate their contracts - which allows the employer to influence a "best contract" thereby choosing a winning union; thus a union can't fall too far out with the employer for fear of being supplanted by a new union. Even though the employee remains the voting piece, they lose an awful lot of power.