[2022] So…the Delny is a mystery to me.

Delny plays very well as an open-water gunboat.
15.8km range with Main Battery Expert means you can juke and doge return fire while basically getting free damage and fires on BB's and heavy cruisers.
If you do find yourself in a gunfight with another DD - your 50mm side plate will shatter even most cruiser HE and your ballistics make scoring hits very reliable even against French DD's.

You just can't cap contest or bully other DD's very well and you don't spot things particularly well if you're not firing.