I've had this discussion with friends and family who teach. None of them can make a convincing (to me) argument that a school administrator is any more likely to be capricious or unfair than managers in the private sector.
Then, the friends move onto the whole "how do you evaluate a teacher?" to which I respond "how do you evaluate a programmer?" Sure, there are metrics for both, but none are foolproof. At some point, managers have to go with their guts.
For a variety of reasons, really stupid metrics in tech have mostly not had staying power, which reduces how much of a problem people consider them to be. Plenty of companies have attempted to institute some kind of LoC or normalized-LoC or other such system to measure programmer productivity, and they are mostly ridiculed as laughingstocks of the profession. Whereas the dumb, unvalidated metrics seem to be actually making inroads in education.
To some extent tech benefits from there being giant piles of money everywhere, which limits how much leverage stupid employers have over their employees (where legal, they try to use noncompetes to counteract that effect).
An interesting feature of this decision, though, is that it interprets the "right to education" in the state Constitution as creating an enforceable, quite broad right, rather than merely a general principle: any government policy that stands in the way of students receiving an effective education is (according to this holding) unconstitutional. If that stands as precedent, students may have another way to combat poorly designed metrics: such metrics might also be unconstitutional. (One problem, of course, is that there's no clear limiting factor for this principle; it essentially empowers judges to make policy decisions about what stands in the way of good education.)
You evaluate a programmer on the coding problems they solve that contribute to the business.
There is nothing so clear for teachers other than their class performance on standardized tests, but standardized tests measure only a very limited part of what a good teacher should be able to offer.
This is how you get lots of low-hanging fruit pickers, rather than programmers who would rather solve hard problems for more significant, but less visible, business needs.
Examples: Refactoring is effective in the long-term but doesn't look as good in the short term. Exploratory work often takes time but doesn't show any specific productivity. Teaching and helping others is incredibly value, but increases their productivity rather than your own.
Evaluating programmers by their business output leads to low-quality code run by a team that doesn't talk to each other and loves self-aggrandizing. Also when something big finally does slip through the cracks, everything will fall apart.
And if you want to find outliers with it, good luck - they'll make mountains out of their molehill of work.
Honestly, it's not very easy to get good metrics for programmers - for the same reason it's not very easy to increase programmer productivity on a project. It's not easily divisible work and involves a lot of teamwork.
Two reasons:
1. Evaluating people by "solved problems" encourages them to solve problems rather than do other kinds of work - which is often more important.
2. You can't evaluate people by their real performance - only their perceived performance. You're splitting them up individually to do so as well. As you are a human being, your perception is biased and your information is incomplete - there are many, many people who would take advantage of that to make their work seem more important/better. Hence, self-aggrandizing.
If you want people to do their best, give them the power to do self-evaluation and ask them to find ways to improve their work/their team's work.
If you want to fire people, your absolute worst employees - the bad ones who somehow survive layoffs, are the ones who are going to abuse your perceptions and metrics the most. The only way to get around this is to gather metrics in ways that can't be self-reported or influenced by the individual being evaluated, even indirectly, except by being competent at their job.
So how do you prevent that while also not making it impossible to fire people who insist on teaching young-earth creationism or abstinence-only sex ed or whatever else wrong/harmful you can think of?
Honestly, it is a pretty bad solution. However, it was sufficiently shielded from politics that bypassing that shield was difficult for decades.
Pretty much any alternative is purely governed by populous whims because it is no longer the "norm" but "some unique thing we do".
Now, if you can get a constitutional amendment passed that solves the things tenure is truly needed for [such as abuse of position to engage in de factor or outright bans of topics like evolution]...sure. I can see a better solution there.
However, I don't see a better solution happening :/
And I'm not sure how the problem you describe is limited to public schools? If my manager doesn't like me (for whatever reason), he can find a way to have me removed from my job. Nitpick every minor problem, make-work assignments, untenable deadlines, etc.
Why is it incumbent on your friends and family to demonstrate that school administrators would be more likely to be capricious or unfair, and not on you to demonstrate why it's a good idea to subject teachers to any increased level of capricious or unfair management?
Then, the friends move onto the whole "how do you evaluate a teacher?" to which I respond "how do you evaluate a programmer?" Sure, there are metrics for both, but none are foolproof. At some point, managers have to go with their guts.