Not just that, but the union would likely end up capping their salary much lower so the wealth can be spread around. How hard is the 10x engineer on the team going to work when the compensation is the same regardless? This is where people end up working multiple jobs, if they can keep up with their peers only working one day per week.
That's right, no more "10xers" working 80 hr weeks making those who can't or won't look unproductive.
Couldn't unions just follow actors' guilds and the like where there are no salary caps?
I find it hard to believe workers would vote for a union to lower or cap their wages. That feels like a total straw man.
In my experience unions suck when they overemphasize fairness over real world practicalities (see almost anything seniority based). They don't have to be that way.