I feel like a lot of that is due to Toei's mishandling of the anime to put it lightly. We're entering the protracted end game of the series. I imagine from the end of Kaidou onwards series interest should start ramping up much like in the run up arcs to the WB war as we start the run up to the finale.
The "bad" ratings for both shows have nothing to do with them getting bad themselves, but rather that Kamen+Sentai run on the same timeslot AND the most important part it was sports festival season in many places in Japan. It rained on Saturday and many events where pushed to Sunday so kids missed out their Kamen/Sentai/OnePiece/Dragon Ball