I think you're quite confused. Emacs always avoided a huge startup hit by loading elisp code into temacs (bare bones emacs that only exists when building it) and then dumping it with unexec to produce the emacs that is distributed. A decade ago, glibc stopped supporting unexec and emacs had to switch to a different method of incorporating the elisp code and avoiding the startup time, but the unexec code was still there. Now, a decade later, that code--which was not being used--has finally been removed.

None of that has anything to with emacs vs vi -- the point that your professor was making was that vi was distributed by default with UNIX so it was always there, whereas emacs needed to be installed (which wasn't even an option on servers).