With all due respect an RSS feed is not "your" data, it's just data that you aggregated. You're not comparing it to the fediverse in good faith. If you must make a comparison you can do it with email: do you have an email address? Do you trust your email provider with your data? It's the same with ActivityPub based servers.
Tweets are microblogs. RSS technology is fine for publishing them. The Twitter client only needs to be an RSS reader. Replies, retweets, and likes are empty calories for end users. They're the engagement bait social media uses to power an attention economy.
The fediverse copied the wrong features. There's no point for it to have an attention economy because no one is monetizing the attention. Therefore there's no need for the empty calorie features, and no need for my data to be on someone else's server.
And you're free to pick a mastodon instance that offers the same (if that's something you cared to do). Do you also complain that it's possible for any rando can spin up their own email server and start passing out free email addresses?