Seriously, the moment you are on a "secret" one-to-one with your boss you have already lost. There's reason why unions have always bargained collectively, and there's also reason why bosses have always tried to avoid this.
If everyone in the union gets X% (with or without a seniority bonus), why would anyone give two shits about putting an effort in beyond the minimum.
You want a taste of what a software dev union is like in the US? Join a government organization where income has almost no correlation with performance and you'll be ready to put a gun to your head after 6 months due to the glacial pace people work at (assuming you want to get things done efficiently).
People don't have an issue with collective bargaining, they have a problem with the other negative effects of unions.
The things that are happening Disney, Edison, and a lot of other places shouldn't be tolerated by software devs collectively.