I would say no, until we get a confirmation on it.

Is it just me, or does every single episode of Ryuki end on some kind of cliffhanger? Is there any plain filler in it at all that doesn't build on the story?

There's only really one episode that could be considered standard filler. Other than that all of the episodes pretty much add to and build the story.

There are a couple that come close, but the main character in them becomes a regular so even then there are consequences.

Is Kamen Rider more watchable than Super Sentai?

Everyone complain about Super Sentai have a same and predicable storyline while Kamen Rider take more risk than Super Sentai.

Am I right?

Your mileage may vary.

Some people prefer Kamen rider over super sentai and vice versa.

No. Your original question is entirely subjective.

And it's not that Super Sentai isn't prepared to take risks, it's the fact that the last time they did it things didn't turn out well. It may be 3 years on but Go-Busters is hardly forgotten.

No, you're not right.
Sentai is more formulaic, but both franchises tend to take plenty of risks.
The difference is because Sentai isn't dipping into pseudo-drama beyond minor story arcs, some people (Notably people not watching a particular series, only getting second hand info) tend to see Sentai as repeating itself.

THIS. Most people who complain about Sentai being always the same don't even watch it. And Kamen Rider is awfully formulaic as well. It's just that the character structure can vary a bit more because you don't have to have a team of heroes.