Pronunciation of Greek words such as KOINONIA

[creationist]

I am of Greek extraction and  I’ve been reading and writing Greek ( basic) since I was 5 or 6. (I’m now 42).
In Greek gramma, when the letters “O” and “I” are joined (OI) are pronounced “I”.
Also “E” and “I” (EI) are pronounced “I”.
Don’t ask me why, I think it’s just one of those spelling things to distinguish plurals from singular and also similar sounding words with different meanings.
There is also the “EU” pronounced “EV” or "EF".
“AU” pronounced “AV” or "AF".
“AI” pronounced “E”.
"U" sounds like an "I" if another vowel doesn’t proceed it. Musterion is pronounced misterion (mystery)

Using these rules, the word koinonia is pronounced kinonia in Greek.

“Eidolon” pronounced “idolon” (idol)

“aichmalotos” pronounced “echmalotos” (captive)

“Euchimai” pronounced “efhome” (I hope)

“Eulogeo” pronounced “evlogeo”(Bless)

I have asked a friend who studied ancient Greek, Greek history and Greek Archaeology who says that as far as he knows, these rules applied back in the ancient days also.

My question is why is koinonia  pronounced so and not kinonia? And why are many other Greek words pronounced so by learned scholars?
Been able to understand Greek, it gets confusing when I hear sermons by learned when they pronounce these words incorrectly.
Are they teaching wrong pronunciation in Bible school or is it just an agreed standard ? Or am I just too pedantic?

[Broken]

As far as I've been able to gather, its because modern Greek is pronounced differently to ancient and koine Greek.

Same way that English today is pronounced differently than Middle or Old English was.

Of course it is quite difficult to figure out how words were pronounced if they're just written down - I know that with English, we only know from rhyming poetry. But you don't get rhymes in ancient cultures - and they're modern in English, so maybe they're working to an agreed standard.

Just be thankful you're not using Egyptian - they had to completely make up pronunciation and vowels for it and have no idea how it was really said!