Does the fact that Abdul took over the sweeping duties from Radhakrishnabai imply that her service was found to be unsatisfactory?

There is no indication in the text that Radhakrishnabai's service was unsatisfactory. In fact, Chapter 35 praises her work quite highly, describing it as 'clean and prompt' and posing the rhetorical question, 'who else could match her?' The text merely chronicles the succession of devotees who performed this humble service. It states that Radhakrishnabai performed this work, and then 'Later, after some time, Abdul moved forward in this.' This phrasing suggests a natural progression or transition over time, rather than a replacement due to inadequacy. The chapter celebrates the selfless service of multiple devotees, including Balaji Patil Nevasakar, Radhakrishnabai, and Abdul, as examples of pure devotion.