The only time the openings well and truly spoiled something was when they gave away that Robin was going to be with the crew way before Alabasta ended. (And they've learned that lesson.)
Most of the other stuff is only spoilery if you KNOW it's a spoiler, otherwise they come off as random action shots made up for the opening, like when the monster trio fought the admirals.
Without context a given shot usually doesn't mean much.
I guess it gave away that Kaidou was a dragon but that was suspected way in advance anyway and revealed pretty early into Wano.
And Kyoshiro being Denjiro.