I am getting so tired of seeing this completely unfair question, whether it's for Sentai, Kamen Rider, or ANY franchise.
NO!
None of these franchises are getting weaker with the times. They are ADAPTING to the times, and if any of us want to call ourselves fans, so should we.
It's not really fair to compare old stuff to new stuff. If you do that, of course you'll see things they don't do as much today. From how they film fights and choreography to plots and characterizations. Things change over time. The industry changes. What's allowed on TV (especially a kid's show) changes. Sometimes there may be more limits on what they can and cannot do, sometimes the toy companies put their feet down and say "throw all these toy promotions in there!", but all that is just a challenge to see how creative the writers and the actors can get. True creativity can find its way around limitations. We as fans need to stop being so judgmental and adapt with the times. If we keep expecting things to go back to the way things use to be, we're only going to get disappointed
every time. That's not how things work.
Maybe it's not the best example, but look at me! I keep my expectations low. All I want is to have fun with what I'm watching. That's all. And often times, the series I am watching will deliver on that and then some. And if we haven't watched the show in its entirety, then we shouldn't judge it as a whole. I don't often watch Power Rangers, but I do my best to make it VERY clear that I stop because "it's not for me". I don't stop near the beginning and claim the entire production to be crap just because
I don't like it. Who am I to make that kind of judgement call? Who is ANYONE to make that kind of judgement call?
Me. The past few years have been rough for the franchise, but it's not like Kamen Rider's in any better shape. Drive was even more painful than Ninninger.
I second that.

I don't know if Super Sentai really is the best, but I like to think of it as an acquired taste. Kind of like how there are fans of Superman, even though most people think of him as the Gary Stu of superheroes.