The question is about the etymology of the word ‘lion’. My research informs me that the word is derived from the Latin ‘leo’ and Ancient Greek ‘leon’. Leon is also a first name for people of Greek origin since ancient times. Leon appears to have preceded the Latin ‘leo’.
It seems to me that a lion is called a lion because Ancient Greeks called this impressive big cat ‘leon’. Over about a couple of thousand years and more the word evolved in the English language to ‘lion’. Only one letter changed.
I am not an etymologist but perhaps English people mispronounced ‘leon’ as ‘lion’ and the name stuck.
The German word for lion is löwe. This is derived from the Middle High German lewe and from Old High German leo and from Latin leō.
SOME MORE ON THE LION MANE: