It's actually even easier than using Save As to see the full path to the currently open document. Just do a "Secondary click" on the document title in its window's title bar.
Like you, I relied upon Save As my whole life to check a file's location and considered it a must-have capability. Turns out it's even faster to use the single-click method to reveal the full path to the open document. It displays the entire path to the current document starting from the level of your Mac, and works for files stored on drives as well as iCloud.
If you're not sure how to do a secondary click, go into System Preferences, select Trackpad, Point & Click to find the current preference for secondary click on your Mac. If you happen to have a mouse with more than one button, it's probably the right button. As a trackpad user, I check the box to "Click or tap with two fingers," so a simple two finger tap on the title of an open document reveals its full path. This feature actually has been around for a very long time.
Note that this is not the same thing as the Autosave and Versions menu, which is exposed using a little drop down triangle to the right of the title. There is no visual clue for the presence of this feature - you just have to know it's there, probably because this feature goes all the way back to pre-OS X days.