It's also possible that Marston felt a lot of guilt over something or enjoyed being humiliated for whatever reason (he "deserved" it). Or possibly this was all his fantasy written out and nothing like this really went on in his life-- an awful lot of escapist fiction is like that.
I'm sure there have been many messages of empowerment and self-realization in WONDER WOMAN since at least the 1970s (however well done or not). And maybe all these scans focussing on imprisonment and punishment are giving a wrong impression.