In other words, I am trying to make the point that for etymological purposes, a profound
knowledge of other, related languages is a must.

Up to a point.....

It depends on your level of interest. I studied at a public school in the UK. When my friends were off playing 'soccer with the lads', I was out playing 'cricket with the chaps', lol

Latin and French were the two foreign languages that we had to study. I hated French with a passion yet loved Latin. To this day I love to explore the Latin influence in English.

French may have influenced English, but I believe it is more recognisable than the Latin influence.

For example, a NES may instinctively know that the word 'cuisine' is French, yet not realise that 'etcetera' comes from Latin.

Why do fish, ducks, chickens, rabbits etc have the same 'name' when they are alive as they do when they are on your plate, yet cows, sheep and pigs become beef, mutton and lamb. (Rhetorical by the way, I don't need an answer)

Then there are the more profound questions such as;-

Why do we say a 'Free Gift'? Aren't all gifts 'free'?
Why is the word 'Phonetic' not spelt phonetically?
Why is it that when you buy a bigger bed you have more 'bed-room' but less bedroom?
Who originally put the alphabet in 'alphabetical order'?

Why do we now have the pronunciation correlation between 'to, too and two' when the word 'two' used to be pronounced as 'twoh'.

If you want to try getting your tongue around difficult linguistical grammar and pronunciations, try Welsh, haha