They do rule on factual matters. But it has nothing to do with the truth (well, we
hope it has
something to do, but there's no guarantee whatsoever), it's just legal action. They can rule sun rises on the west, but it won't change the movement of the sun. They can rule somebody is a murderer, but whether it's the truth or not is not determined by that ruling. It could be either. The legal consequences are determined by the court ruling, but the actual murder doesn't change. We hope that in most cases the ruling coincides or at least resembles the truth, but we know for a fact (and this
is the truth) that is it not always so.
> Every human being and every institution has such limits
That's exactly the point. So we shouldn't act like these limited institutions suddenly gained magic capacities because we conducted some complicated procedures involving some highly paid people.
> But if your point is that courts are useless when it comes to arbitration of the truth
No, they are not useless. They just aren't the truth, they are implementation of a flawed process that hopefully leads us closer to the truth than any of the other the alternatives we could find. It's not binary - it's either whole truth or useless.
> There may be others but most institutions are going to converge on similar functions
There are other models. I wouldn't claim they are better or worse, but they exist. I would recommend checking out: https://www.goodreads.com/book/show/30066446-legal-systems-v...
Are any of those better than what we have? Who knows. Maybe we had the luck of finding the best one. Maybe in 200 years history enthusiasts would be laughing at us idiots subjecting themselves to such obviously flawed and useless system.