I agree with both the original poster (and other drivers for improvement) and the apologist of the status quo.
Calibre is a useful, powerful, feature rich application as it is AND at the same time it definitely could use some serious usability overhaul. As good as Kovid and other developers are, they are programmers and that fact alone makes them less than ideal interaction designers. Also Calibre is being developed using Piece Meal Grows pattern and it does not really lend itself to easily creating great usability.
If any of you are really interested in this subject and want to improve Calibre, find and read these two books. You will understand what USABILITY and Interaction Design really means. How and why some things excel at it and some are just meh (Calibre) and some really suck at it.
"The Design of Everyday Things"
by Donald Norman (father of usability as field of expertise). You will look at the world around you, especially at manmade things with different eyes, forever. I could not put it down - read it in one day.
"The Inmates Are Running the Asylum: Why High Tech Products Drive Us Crazy and How to Restore the Sanity" by Alan Cooper
And you will see why developers are at disadvantage when creating good interfaces. It's not their fault. In this book Alan (one of the most prominent figures in interaction design) describes two kinds of humans: Homo Sapiens (normal people) and Homo Logicus (developers etc) and the differences between these two species. Their needs & priorities when using software and their behavioral patterns when dealing with the other kind.
Come back to this thread after you've read this book particular, you will understand all view points but ... you'll see
These gems are really fun to read and will truly change your lives - especially if you are developer with ambition to write great programs rather than just useful.