I like the option of having tabs on the left but it would be a better experience if the toolbar on top was removed when that happens. Orion's implementation seems unintuitive. Let me explain the 2 options that are more intuitive to me.
Safari's implementation of tabs in toolbar where the URL bar is for the active tab

Arc's implementation where the tab bar is on the left and no toolbar (shortcuts to get to URL bar)

With Orion's implementation, opening a new tab (in the foreground or background) makes you wonder where the other tab(s) went. When users see the URL bar, they expect to see tabs as well. If you are moving the tabs, hide the toolbar as well so users
I would expect that when a user enables tabs on the left, the webpage takes up all the space on the right.
Check out how Arc feels when using it throughout the day. It seems very natural. Something that would benefit Orion users as well.