What I find so entertaining about this chunk of history is how this new way of selling and consuming books oscillated wildly between Very Low Art (“Penny Dreadfuls”) and Very High Art (classic (hence out of copyright) novels, Shakespeare, etc.). Low Art created the format. High Art discovered that it could use the format.
My Dad collected Penguins before and after WW2, and probably also during. I still have some of those. None of them were Penny Dreadfuls.
Also interesting was the claim that paperbacks are now thriving, better than ebooks are. My suspicion about that one: give it time.