This is very interesting what you are doing!!!
One thing comes to my mind : in most of the cases (and I think it is valid for any type of searching tools), it's thought for people who know what they are looking for. But when you do researches in art history about a particular subject, you don't always know what you are looking for and sometimes you only know what you are not looking for. But tools, in most cases doesn't allow to search "without a criterion".
For instance, I have a website in mind (but it doesn't concern art at all) it's LinkedIn. When you search a job, it suppose that you know where you want to work. In my case, I'm looking for a job in UK but I don't know where except, I just don't want to work in London. I cannot select "UK - but no London" in the search bar...
I noticed this pain point when I was writing a thesis in art history and academic people often visit galleries website without knowing exactly what they are looking for :)
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