I'm a coder and have been using slack for years with success. Not one single one of your complaints has ever been an issue for me.
Whenever I want to post a code snippet, I just use the triple backtick technique, like:
```
code goes here
```
You can also insert code in the middle of a comment with a single backtick around it: `like so`
For the most part, though, I keep my code in the Git repository, and it's pretty rare that I actually need to share a bunch of code in Slack messages. If I want to pair with another developer I just open up Tuple or Zoom and do a screen share.
Syntax highlighting in a message is really powerful if your message includes a series of diffs.
```diff
- Remove this line
+ Add this line
```
But even if developers are fine with highlighted code snippets inside message, that still leaves the buggy snippet tool which adds newlines when you copy-paste from it, not enumerated, or bulleted lists, no hyperlinks except verbatim, etc. The no hyperlink part is annoying if you have to link a couple or more long urls and placement matters.
Edit: To add to the list, since slack doesn’t use real markdown it is impossible to included backticks in code samples (e.g. `` ` `` is not a thing, and neither is ```` ``` ````).
Yeah if I feel like my snippet could benefit from syntax highlighting I’m probably doing it wrong. I can’t imagine other people would appreciate my giant walls of text/code in a chat channel. I can use a gist, screen share or link to a specific line in a repo if I need to.
Code snippets: Slack does not allow you to type put highlighted code snippet in a middle of a message (you must import them in a separate message).
Code Snippets: If you import code snippets using the tool, you cannot simply copy paste from it. There will be extra new lines and other noise.
Links: Slack does not allow you to put a hyperlink except verbatim.
I’m sure there are more. But slack is a pretty lousy chat client with poor support for basic needs of developers of code.