The basic principle is everyone gets the same pay, meaning if you are someone who wants to put in a lot of work to rise up quickly, it won't happen.
This isn't true and I don't know where this idea comes from
according to anti-union propaganda, that is.
(sure, that could be what the result of negotations is, but it doesn't have to be)
I don't know how things work in your country, but here in europe union sets minimum wage for a position/skill level. If you work more, you get paid more in overtime pay, if you are more skilled, usually you have higher wage.
And atleast in my work, everyone is paid more than minimum.