Drowned do not seem to take any extra damage from an Impaling trident, despite the fact that they are underwater mobs.
To test this, get a trident with Impaling V. If you throw at or hit a Guardian with the trident, it will die in 2 hits, whereas with an unenchanted Trident it dies in 3 hits.
However, if you try the same method on a Drowned, it dies in 3 hits from an unenchanted trident... and still 3 hits from the Impaling V trident.
I learned that MC-128249 was originally about dolphins but was later changed to drowneds. So in that way should this MC-129940 be marked as a duplicate of that one? XD