Yes, I think it's because of the way Takeuchi developed Sailor Moon that she also mentions in this interview. If she had just gone with the plan to adapt Sailor V, she would have had a head start and maybe could have taken it more slowly, like how other mangakas do when their work is adapted, but she insisted on creating a new story on the spot, and specifically one with many characters and plot elements, all while having to pump it out as fast as possible to allow the anime to continue.
I guess you could say she just aimed too high from the start and she was bound to become overwhelmed sooner or later, but I'm glad she did so because while I like Sailor V, to me Sailor Moon elevates that story and, much like Osabu, I feel like its fast pace and the often vague backstories can even be seen as positives in how they make the manga more mysterious and fun to theorize about. Plus like Takeuchi says we still have the anime (and now PGSM, musicals, etc.) to pick up the slack for some things she couldn't do, so in the long run the way her manga is told has allowed different adaptations to continue to be creative.