One thing I always found neat about Dynaman, Bioman, Changeman, and Flashman was how all four shows had a multi-episodes arc where the villains gain a power-up and become stronger, and the heroes were creamed, having to train or prove their worth, and acquiring their own power-up. They acquire new moves, and that’s it. It’s completely for the sake of the story.
They don’t get armor, a new ranger or ally character, new Bandai-approved weapons or several mecha, there was no merchandise to be gained from these story-arcs, it’s something that naturally came from the progression of the story and the battle escalating.
So, eat that, people who say “Sentai was always about the toys.” :p