I think probably my feeling about it currently is that the search engines are now quite different (and complementary) in their search functionalities and results, and so they really serve different purposes.
For example, use NZB.su for searching categories in a low-spam, release-driven environment where multi-select isn't needed; use Mysterbin when you really need to verify archive contents; use NZB.cc when you want to do a search by relevance; use Binsearch when you want to search on a poster name and are happy to deal with ony loosely grouped results (needing multi-select), etc.
Notice how on your screenshot (helpful btw) that you have an option to sort by relevance, but only one engine actually supports that; likewise the column for filename ...
Currently you can set all your preferred search, sort & display options on the different tabs, and then just use the Global Search to pass a string to each tab and run the query. I can't see how functionality could be improved much more than that, tbh.