A key problem in the US is that in a unionized job you are legally required to be represented by the union. Union membership is non-voluntary.

If you think you are part of that top percentage or even if you think that the union is not representing your interests, tough luck. It is illegal to quit or reorganize like-minded individuals to form your own that better represents you. To reform the union you need to get 50% of the members to vote for change instead of just forming a new, smaller organization that represents your interests.

This is in contrast to many European unions where you can choose to join because you think they provide worthwhile benefits. Or you can choose to not join because it does not. Unions need to compete on benefits to their members and are thus incentivized to provide better benefits.