I've used LyX for a very long time. It has the best graphical equation editor I've ever used: it natively supports all of the complex structures you'd want, can be used incredibly efficiently via the keyboard (e.g. tab-completion and tab-navigation), and is still incredibly discoverable via GUI.
In general, it's just a very pragmatic layer on top of LaTeX. I've done a lot of complex ad-hoc formatting in it as well.
I like, that one can define macros in LyX. For example I wrote a simple macro that looks like "paren(thing)" which is then translated to "\left(" thing "\right)". This makes it much easier to write formulas, because I don't have to keep track of parens at all. LyX in this way makes it more convenient to write TeX/LaTeX.
On the other hand, you do get the full (La)TeX ecosystem to draw on. If I want to draw a commutative diagram, I can add tikzcd to the preamble, and insert inline TeX to do so.
There is some support for the LaTeX ecosystem from within TeXmacs. If you want a TikZ drawing, you can insert it programmatically into a TeXmacs document in a seamless way---if you have the same font for your TeXmacs document and for LaTeX it will be nicely integrated as far as I know,
You can see the blog post
https://texmacs.github.io/notes/docs/embedding-tikz-figures-...
In general, it's just a very pragmatic layer on top of LaTeX. I've done a lot of complex ad-hoc formatting in it as well.