I don't know of any alternatives, free or not, OSX or not.
I don't see why overkill is a problem.
I suppose the GUI is a matter of opinion. I for one enjoy it a lot, possibly because I focus on the functionality. But you aren't the first person who has posted about a lack of polish.
(Hey, not everyone has expertise in GUI design and Apple UI standards
and calibre is primarily developed by one person. I'm sure no one would object to more polish, if someone volunteered to do the work, but no experts have ever stepped forward...)
If it isn't working properly on your computer, that is either a bug or a misconfiguration of some sort, either way it shouldn't happen!
What exactly isn't working?