> the wide range of functionality on the site can feel overwhelming and difficult to understand I guess it must just be my lengthy history with the web, but this line is like nails on a blackboard to me. It's OK to have to learn how to use powerful tools!
A mainframe-style UX where you have to type magic letters to trigger functions is great once you've gotten used to it, but the average user will not put in this effort and simply use something else instead (compare e.g. vim vs. nano). You can afford that sort of UX when you have users who don't have much of a choice and/or will spend a lot of time using that specific tool (which is why vim is still a thing). That's the case for e.g. airline booking systems for agents, not the case for airline booking websites for average users, and not the case for Wikipedia either.
The best UX for this is a UX that is simple, yet still provides the advanced features, and ideally makes them discoverable. A classic example would be menus: You can either slowly click through the menu with the mouse, you see all the options, and you see the underlined letters that will allow you to navigate the menu much faster if this specific menu is worth learning.
Additional visual clutter can be overwhelming, even to experienced users, especially if it's not well separated from the important stuff (it can simply make the important things harder to find - compare e.g. the toolbars of Google Slides and OpenOffice Impress). But good design can easily counteract this. For example, you could use a grey background on the unimportant stuff to let people focus on the important stuff.
Which is why Wikipedia is doing. It's not as if the presence of that toolbar is going to distract someone from the only other task that can be done on the page, reading the article that takes up the entire rest of the screen...