Seniority is about the biggest thing in a union contract
It's also one of the biggest flaws, too. I'm not in a union, but work in a union shop every day. The new guys with ambition are typically at the mercy of the long-time guys who know what they can get away with - some of whom are still employed only because of the union. I understand your point about and have seen the promotion of "butt kissers" in open shops, but I've also seen the lazy slackers - regardless of how long they've worked there - get the first walking papers when times get tough. With the union, these employees are like herpes: the company can never get rid of them, while the ambitious FNGs that want to work are put out on the street first if cuts need to be made. It's stupid.
And it's one of the reasons I've declined direct employment where I am now several times; working 2nd shift until the second coming isn't high on my list of things to do, as well as being target #1, regardless of how hard I work, if we have another dip in the recession.