Sentai toys have been horrible for years. The mecha designs look worse as the years go by. Gosei Great and Zyuoh-King look like gods compared to any of the Zenkaiger or Ryusoul Mecha. The henshin devices are too goofy and overly complicated. What happen to wrist changer and just pressing a button?
From what I heard, mechs have never sold as well as the cosplay toys in Japan, and the price of raw plastic to build toys with always seems to get higher and higher. So as profits drop and Bandai feeds less money back into toy design each year, they increasingly concentrate on the big ticket item.
As for the wrist changers, they are from an era when the most common piece of technology you would find on someone's person was a digital watch on their wrist. Transformation items tend to get based on items that people might commonly carry around with them (it even sometimes applies to the collectables i.e. key based gimmicks).
As cell phones became more commonplace and people started to stop wearing watches, transformation items increasingly became based on phones. And then, because I guess phone design has homogenized into rectangular bricks, collectable widgets have become really popular with little Japanese kids, and they want to keep things different from year to year, it's become a free-for-all of more complicated designs.
I'd expect future Sentai to be increasingly trying the kind of wild toy concepts that Ultra has had in recent years, to try and climb back up those rankings. They're still one of Bandai's ten most profitable toy brands, but they need to catch kids imagination if they want Bandai to put more money back into the show again.
