It is not nearly as bad anymore as it used to be. Think about the Showa era where we could get 4 episodes of great development for one of the characters, and the remaining 46 episodes would be pure filler.
I like KR Black and everything. But come on, that show would only have been 12 episodes long if we took out all the filler.
Showa era still had things like most of X and the second half of Stronger though... Even Skyrider has a surprising amount of continuity once the first villain is beaten, although it's still clearly a monster of the week show (and that continuity stops after a while).
im just speaking for the kids mindset not adults, it just seems kids rely so much on toys rather than watch filler episodes to boost up ratings on episodes, if you know why because they always want something new to buy and when they get that, they watch the episodes for their debuts, it's part of motivation and fun for them. im not saying after the final toy end the series, what im saying is make at least 5 episodes of making the story interesting to end the series.
I was just replying to your mention that the show stopped using switches.
Anyway, regarding your general idea. Toy debuts do seem to help ratings with children but they're hardly the only factor. Fourze's ratings with children only really got bad by episode 40, not 33. Cosmic's debut really didn't give a boost to the show at all with children, even though the ratings were decent, and Meteor Storm's debut actually had fairly low ratings. Oddly enough, the first episode of the Capricorn arc actually had Fourze's last big boost with children.
As far as Gokaiger goes, the Go-onger arc with the new engine had a boost with children, but the actual final robot combination had a
drop and its ratings with children had gotten bad by episode 22, a long time before they stopped adding new toys.
Now, there IS a trend of Riders' and Sentai's ratings with children dropping in the last 10 episodes, and those episodes also are the ones that stop introducing new toys, but I'm not really sure what's the cause. Fourze even tried to reintroduce Rocket States at that point, but it didn't really help at all.
I think there might be multiple reasons though. The ratings dropping in the last quarter isn't something new, but, if you look at older shows like Kabuto and Den-O, they also had ratings drops with children around July and August, which match the ending of the series now, recovering by September (before going on to drop again during the final 8 or so episodes). So, in addition to the usual lower ratings near the ending of the show, the current rider series also have the same period in a naturally lower rated time of the year. I guess it's related to school vacations or school tests?
Alternatively, maybe Toei stops marketing the tv show much by that time? It could influence those numbers, considering how they'd be preparing to market a movie and the next show. It could also explain why those early Heisei series had a ratings drop there too, the August summer movie's marketing replacing the tv marketing for a while. Of course, the lack of toys also means even less marketing now near the ending of the shows.