Correct, iexplore.exe is itself a small wrapper. But that doesn't stop Microsoft from not shipping that small wrapper. Software that embeds mshtml.dll does not require the existence of the exe file.
(Or alternatively, Microsoft could put some hack into Windows so that attempts to run iexplore.exe are passed to Edge unless the administrator has twiddled with some arbitrary registry key or group policy.)
IE should just be a compatibility mode in edge so you only have one program and a button to say "this page is broken, load in legacy mode". That way everyone else in the world can stop being forced to support IE users.
(Or alternatively, Microsoft could put some hack into Windows so that attempts to run iexplore.exe are passed to Edge unless the administrator has twiddled with some arbitrary registry key or group policy.)