My dad is having similar issues with a home he's building in Florida.

They built the deck with 16" centers between joists. He recently became aware of the 12" center standard. Factory spec says up to 16", but he dug in pretty deep and 2 of 3 comps he found had sagging issues. Now this was Florida beach front stuff, so the elements have a greater impact than here. It was a big enough issue that he dropped several grand scabbing on 2x4s to either side of the joist to cut down the span by 3&1/4". Keep in mind, he's an ocd engineer and this is for high end rental where bowed decking is unacceptable.

You may consider an option like he did. Or just let it ride. Definitely would not rebuild the deck.