A yesteryear superhero with waning superpowers must mend his ways to reclaim lost glory and deliver the doomed planet from the hands of a cunning corporate kingpin.

Agreed, add in an addictive ingredient the corporate bad guy is adding to the food and it’s perfect.

I think that idea works, I like the idea of an over weight culture, the bad guy would be selling the populous the delicious but bad for you products.

I believe this idea has potential.

What if the former Superhero has old school values, ‘Truth Justice and the American way’ and also believes in fighting fair. (Think old school superman)

Meanwhile the new superheroes are brooding and dark and believe in defeating the bad guy by any means necessary. (Think Nolan’s Batman)

Now the Corporate King pin has bought off the new school superheroes and the old Superhero must face the man he trained to take his place who’s now turned to evil.

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When the Justice Squad is bought off by an evil trillionaire, a former superhero with dreams of past glory must face his now evil protege’ if he’s to defeat a cunning corporate kingpin who’s evil plan will doom the planet.
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Hope that helped, good luck with this!

Not a bad Idea, I would drop “Mend his ways” since it tells us nothing.

If you had said, mend his ways as a hard drinker, mend his ways as a womanizer, or something such as that, then I think it could stay.

Also I don’t believe you need, waning superpowers, saying a yesteryear Superhero is sufficient.

Finally I might mix up the last line just a little bit,

You wrote: deliver the doomed planet from the hands of a cunning corporate kingpin.
I would write: Must defeat a cunning corporate kingpin who’s plan will doom the planet.

The reason is, in your version the planet is already doomed, I believe it would be better for him to save the planet from being doomed.