Depends on the company and whether or not they actually delete your data or not. 

And it also depends on whether that data has been saved by others before you deleted it. For example Reddit posts were scraped by AI models. The US Government probably makes regular downloads of every single post on Facebook, Instagram, X, LinkedIn, etc.

If the data was publically available for any amount of time, there's a good possibility it was saved by someone.

Although data storage does cost money but the state owns the money printer so that's probably not a barrier to them.

But theres at least a chance deletion will help, over time data can be lost, corrupted, etc. It's better than doing nothing.