Koha has good and descriptive page titles, but according to https://www.w3.org/WAI/tips/writing/ the unique information should be first, before the name of the website (Koha).
This is a duplicate of Bug 26703 - We should reconsider best practice for our title elements.. but it's interesting to know that it's also an accessibility issue.. it adds weight to the argument. I'm going to copy your description to that bug as a comment and close this one as a duplicate if that's OK. I think our first step is to agree to a new coding guideline to ensure new instances of incorrect title elements don't keep working their way into the codebase and then work through fixing all the existing cases.
*** This bug has been marked as a duplicate of bug 26703 ***