Unless you click on a link or a select a text, right clicking brings up the website's custom context menu, not Orion's. A user trying to show/hide the title bar wouldn't intuitively think that there's a different context menu when you select text or a link, so discoverability is low, I would guess. (Version 0.99.124-rc (WebKit 616.1.10))
EDIT
Okay, I just checked again and realised that showing the browser's context menu when right-clicking on a link or selected text is a discord specific feature. So, if a website always shows its own custom context menu or disables right clicking altogether, then there won't be any way to get to Orion's context menu and show/hide the title bar.