Remember also the “Classic Comics” line, which was all the great works of literature condensed to their plot line and illustrated ala Superman. They were great, everybody read them...in fact, I recall a teacher assigning us some great (but boring) work to read and telling us that she didn’t want to find out that we had only read the “Classic Comics” version!
I suspect there were many works that were only read in that version. However, you would end up knowing the plot and recognizing any references to it in later life, so even reading just the comics added to your common knowledge and ability to express our intellectual heritage.
I do remember classic comics, we had them along with the Illustrated Classics. These books and magazines allowed cultural information to be transmitted to all at whatever level... for example the term “great white whale” was understood throughout the spectrum of the populace.