Well, I wouldn't know about filtering by time, as I normally sort by time instead.
As for placeholders, I thought that is what templates do.
Templates are nestable.
I don't know what you mean by "export variants", but templates can be used for exporting from calibre.
"tools" is ridiculously generic. calibre has lots of tools. What specific types of tools do you feel are lacking?
You can modify the translations, see
calibre : Get Involved
I find the help material to be very helpful. In what way do you feel the documentation is lacking? calibre is open-source, including its help manual. If there is some way to improve the documentation, perhaps we can fix that.
But if calibre is really too childish for you, then by all means, you don't have to use it. As an intelligent person, I know that is not a tale for children (and neither for that matter is the regexp guide, or it wouldn't have helped so many people).
Either you will use it and appreciate the quality it does have (despite it not meeting your exacting standards), or your financial needs will figure something else out.
And if you are determined to believe calibre is a child software that doesn't have a good internal structure and whose developer doesn't understand books and how to write good management software, then you may find it hard to attract answers from the people who find it very good management software.
tl;dr
When you start mixing ill-informed complaints with comparisons to other software and how calibre Just Doesn't Measure Up, people assume you are a troll and ignore you. And they're probably right.