Honestly I’ve never really been one to use difficulty level comparisons myself, so I don’t know that I can be much help, I’m afraid! My heart wouldn’t really be in it and I’d second-guess the comparisons far too much.
(I’ve been ending most of these with a line like "I watched this [with/without] [English/Japanese/any] subtitles and feel like it went [completely fine / more-or-less fine / not great oh well] " though and that seems like my best equivalent of a difficulty metric so any Natively person can feel free to mine that somehow if they’d really like 
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@ekg 's the one to tag! Or check out this thread they made. (I don’t honestly know anything about drama CDs )