osascript and AppleEvents
tl;dr : Language components are just dependencies used by the executable and can be accessed through the shell without Apple events.

A: Your argument breaks at a couple of points made in number 2.

a. "The Terminal command osascript does not "know" AppleScript."

Agreed, it does not have all of the languages it supports self contained in one executable.  However, that's where dependencies come in, and when you think of it that way; it's not too troubling that it can access dependencies through your shell like any other application can. 

b. "it passes it on to the AppleScript compiler/interpreter via the OSA architecture by sending out an AppleEvent."


  "When a scripting component executes a script, statements in the script may result in Apple events being sent to applications (developer.apple.com)".


The executable is not limited to only using either code within itself or an Apple event call. Similar to almost every process or application on your machine, it relies on various core libraries and specifically it uses the osa language components installed on your system. It does not use Apple events for passing your script to the language component. 

see supported languages:

❯ osalang 


these language components live here:

❯ ls /System/Library/Components/


Since osascript can access your system's language components directly through the shell, you'll never seen an Apple event triggered just to process/interpret the script input.

for example compare these two commands where the first uses the AppleScript language but does not interact with any other applications:

❯ osascript -e 'set myVar to "hello" &amp; "world"'
helloworld


and the second where we tell terminal to do something:

❯ osascript -e 'tell application "Terminal" to do script ("echo helloworld;")'
AE2000 (63917 ): Sending an event:
------oo start of event oo------
aevt('core'\'dosc' transactionID=0 sourcePSN=[0x0,dd7dd7 "Terminal"] timeout=7200 eventSource=3 { '----':utxt('utxt'(TEXT("echo helloworld;"))), &amp;'subj':null(), &amp;'csig':magn(65536) })
------oo  end of event  oo------
tab 1 of window id 32644


Only the one that interacted with an application, not just the AppleScript language itself, triggered an Apple event.

Read over this article again and you will see how this explination fits now.  OSA Architecture implemented via Apple events is the powerful construct allowing for automating between applications; but interpretation of the input script itself is just done by your system's compatible language component behind the scenes.