> It’s my understanding that in most union jobs, compensation and benefits are strictly based on time in role, not performance.

That is one structure, and it probably was predominant in the past because unions were historically in factories where workers were more interchangeable and had set tasks at a production line station.

Another is more 'guild-like': Jane Smith who is Waitress #2, and Tom Cruise who plays Ethan Hunt in Mission Impossible, are both part of the same union/guild, but one is able to negotiate a much higher salary. But they have the same 'base' level of protection with regards to working conditions, pension, health care, etc.

Certainly Tom Cruise can go above and beyond those 'base' levels, but the union/guild simply provides a floor which everyone is entitled to.

There's no reason why a union contract could not negotiate things like working conditions, health/child care, pensions/retirement funds, etc, but leave salaries out of the collective agreement. Or perhaps have pay bands, with retention/performance bonuses that are out side of the scope of the agreement, and are 100% discretionary to the company: everyone gets a floor, but there's no ceiling.

Unions can be what the workers want them to be. The industrial time-in-role thing can be a reasonable match to industrial industrial jobs. But collective bargaining can include performance-based pay. E.g., the union negotiates the overall base raise and the size of the performance-based raise pool, and then managers decide on raises and promotions. They can also help you resolve situations of individual managerial unfairness, something that HR is supposed to do but is very rarely effective at.

A union is a democratically-run tool. Every tech employee I talk to hates the idea of compensation being based purely on time in role, why would they democratically vote for that to be the rule?

Probably the people who have had a boss tell them they believe minimum performance for a salaried position was 70+ hours a week.

Generally the people who are advocating for a union are doing it to level the playing field for themselves against you.

Nobody has any idea how to properly evaluate that. So they just pick the person who works the least and talks the most, using random jargon to seem smart.