This is straight up misinformation. What saved Sentai was latter half of Fiveman and then Jetman. Turboranger and Fiveman right afterwards sent TV ratings plummeting along with toy sales. The latter half of Fiveman already saw increasing ratings and toy sales. Jetman being a mega hit actually helped prevent cancelation, so much so Saban was originally gonna adapt it.
While it was a massive blunder on Bandai's part to sell of US toy rights, the numbers were already in steep decline.
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It's been an almost continual downward trend since Kyoryuger, long before Hasbro. And once again look at how KR exploded in sales without the need for western popularity.