On a Mac I use "option" for this; much shorter reach
It's funny but I've been using Emacs for almost 25 years and still use ESC instead of ALT/OPTION, guess that's muscle memory from using Emacs via telnet sessions.
Alt+Key doesn't save any keystrokes over Esc+Key anyway, and I think the Esc version is easier to type.
Especially things like Esc : (which is Esc then Shift-;) is surely easier to type than Alt-Shift-;.
That's my experience, too, I guess it's from learning EMACS and its ancestors on actual VT-100 style terminals with no meta keys.
Indeed, never even crossed my mind to set the escape key to meta, definitely not a default even for Cocoa emacs.