No, you don't have to use Safari, which is limited to eight search engines. You can use Firefox, which allows more search engines. Yes, its renderer is the same, but it is different software, and this isn't a thread about the renderer.

I (and I imagine a lot of sysadmin/MSP types) don't care about grouping tabs as much as to be able to log into the same site with multiple login IDs at the same time.

Which also has nothing at all to do with non-default search engine options.