Wait until you find out that absolutely anything can be edited

Ahh, now I understand! I'll try my best to make it less scary :)

To start off

why is there a need for external packages for a text document?

There usually isn't, as long as you only want a simple document. The most basic thinkable document would be

\documentclass{article}
\begin{document}
This is the text in my document
\end{document}

However, you'll likely want a title and author, so you can start off with

\documentclass{article}
\title{Fishes are nice}
\author{Definitely not Jason Mamoa}
\begin{document}

\maketitle

\section{Introduction}
This is a text about why fishes are nice.

\end{document}

You have your "Super basic document", with at title and author. You can make simple formatting changes by modifying the documentclass statement at the top. My recommendation with all the external packages (usepackage) is to look them up one-by-one as you need them. You'll typically find a small handfull of packages that you need very often, and then you'll probably end up copy-pasting those declarations over whenever you create a new document. For most basic documents I'm using like 2-5 packages at most (fancy math fonts, hyperlinks, pretty bibliography, etc.)

Tables are straight up scary

They take a little getting used to, I agree. For someone working a lot with tables, I would recommend getting used to them, but if you only very rarely need them, there are "graphical editors" that let you build a table in a GUI and then give you the Latex code for it. Overleaf has an integrated "visual editing" mode that makes the barrier to entry lower. However I don't really recommend it for someone that really wants to learn to use Latex, because I think it prevents people from progressing past the very basics.

plotting - I didn’t even try to comprehend it

I've used Latex for years, specifically writing documents with a lot of plots. I have yet to attempt to learn to plot directly in Latex. I know some people that will create figures and plots directly in Latex, and I respect them. I use inkscape for figures, and python for plotting, and can get stuff looking pretty awesome that way. Learning to draw/plot directly in Latex is by no means a must.

Please, make it any sort of user-friendly!

As with other powerful tools, I think people are often overwhelmed coming in because of the massive number of possibilities, and the fine-grained control that is possible. My recommendation is to start out with something like the above, and progressively add complexity as you need it. Most people don't require more than basic section (and sub- subsub- etc.) headers, tables, figures, and equations. In that case, you'll need like 3-5 external packages and 3-5 "commands" (stuff like \begin{equation}). If you start out with the above example, you'll probably learn the basics on your own in a couple hours :)

I've held some latex-courses for beginners, so if you want, I could send you the "basic starting file" that the people taking the course have completed writing (with help) after about two hours :) I've been told that most of them feel pretty comfortable learning on their own once they have that.

Yes, I also use Zettlr and it works fine. Especially with the Zotero integration. But you are right, it sometimes needs some tweaks to work fine.