From what I've heard the best option for deleting your data from brokers is: https://easyoptouts.com/

This is just run by two honest dudes and is considerably cheaper than the other services. The reason I like this one (though not used as I don't live in the US, is because these guys are quite transparent about the process.) I've heard numerous podcasts where these guys come into the show and talk about their work. As an example they were on the Firewalls don't stop dragon podcast. I would at least have a look at this service and compare with the rest.

Best of luck 🍀

Podcast details:

Episode webpage: https://podcast.firewallsdontstopdragons.com/2024/12/09/deleting-your-data/

Media file: https://media.blubrry.com/firewalls_dont_stop_dragons/content.blubrry.com/firewalls_dont_stop_dragons/2024-12-09_Ep406_Deleting_Your_Data.mp3

Or am I reading this wrong and this is just because they have to send your data to the brokers to process deletions?

You are reading it correctly.

If they only used your data to process deletions, it would read along the lines of "data shared with partners as necessary to provide (data deletion, etc) services."

It should also normally be followed by a sentence that links to each partners privacy policies, and says that each partner complies with similar restrictions on using your data only for the same purposes listed in the earlier sentence.