With a separate search bar it's possible to easily switch between search engines like DDG, Amazon, Youtube, etc using the drop-down menu. Want to find a YT video or a product on amazon? Just enter the term and click the relevant icon from the list without having to go through your primary search engine first (as I often do when using F.Fox or similar).

It could be implemented so that a new tab opens after hitting Return. Much simpler and faster than how it currently is with the drop-down menu showing search options from Bookmarks, History and your preferred search engine only. Or having to remember to hold down cmd to open new tab when searching from the address bar (unless you open a new tab first).
A search box could be added to the Customize Toolbar pane so that it would be optional.
Thanks