If you want to delete the highlighted text, then why not press backspace or delete? Those already have the explicit action you're looking for.
>> Now, we want highlighting something and pasting to contextually mean "insert markup specific to some markup language, after parsing what's on the clipboard and deciding that it looks like another part of that markup language."
Not really sure what you're trying to say. You don't think they do this already? WYSIWYG-editors on the web almost all have normalization and sanitization built in when you paste something, and depending on where you paste the content will get merged with existing rich text blocks.
I think in general editors should be unsurprising.
If there's a general expectation of "if text is selected, and you do a WRITE_TEXT action, then the selected text is replaced with text"; and if CTRL_V is a WRITE_TEXT action; then doing CTRL_V after selecting text should replace the selected text.
Then again, the above rule already has exceptions; eg writing a parenthesis in some editors will surround the text with parentheses.
The problem here is “you can’t quickly make a link in our wysiwyg”. Screwing paste is not a correct answer to that. Let it detect that a clipboard text is a link and tooltip-hint a user that they can combine it with a selection by pressing ctrl-alt-v, or something similar. Nobody is against your easy editing, but not at the cost of a cognitive overload. I wish UI/UX designers read some books on how human mind works or how to do UI/UX at least.
>> Now, we want highlighting something and pasting to contextually mean "insert markup specific to some markup language, after parsing what's on the clipboard and deciding that it looks like another part of that markup language."
Not really sure what you're trying to say. You don't think they do this already? WYSIWYG-editors on the web almost all have normalization and sanitization built in when you paste something, and depending on where you paste the content will get merged with existing rich text blocks.