Most rich text editors allow bolding running text. "Ctrl+B" vs. "shift-8" are equal.

(Most rich text editors are poorly implemented and suffer from hidden state, but that's a separate problem.)

I use Ctrl+B in my browser to open the bookmarks side-panel though.

Hmmm. To be fair you could also use ctrl+b instead of the markdown sequence.

That's an interesting flow but I couldn't imagine typing like that, formatting while I typed would totally interrupt the thought process/message I'm trying to get out.

My flow is to type first just to get the thoughts out then I format last while I proofread.

I do occasionally go back and add formatting, especially when writing a longer article. I also often add links later, or write [link text]() and fill in the URL later so I don't have to stop and find a reference I know exists. But I add certain types of formatting immediately, in much the same way that when speaking I emphasize certain words in a sentence.

In my opinion, it is about the same, maybe easier to not use markdown. If we count keystrokes, it’s less.

If already typed, it’s less keystrokes to select with Shift+Ctrl then press Ctrl+B.

If it’s not typed, it’s less keystrokes to Ctrl+B at he start and end.

For italics, the keystrokes are about the same with and without markdown.

Perfectly reasonable to have both available: type markdown along the way, map keyboard shortcuts to insert the appropriate formatting characters whether used statefully or with text selected.

I seem to remember that typora works that way.