I don't know what software you are using but, latexmk on my machine takes at least 30seconds to compile a 40 page document with 164 equations and 46 images. Texmacs doesn't have to, it just does the rendering incrementally, references get updated when you insert a new one. You can call an update on the whole buffer, which you normally don't have to, and it updates the same document in less than 6 seconds.

Some important LaTeX packages have workarounds or direct support. For example, you can still render your Tikz images in Texmacs, there is a Tikz repl, but afaik it needs some work. Or just import them as pdf and write the rest of the document in Texmacs.

You can customize the typsetting macros just by altering the texmacs file preamble, similar to how latex has a preamble, so do texmacs files.

No tool will have a standard library as big as TeX/LaTeX when it is created, if that is the bar you set for new software, then you will use TeX forever. That is fine, but maybe better tools can be created, they just require some investment.