I think the walled garden is a flawed metaphor.

I would argue for Twitter over a spotty collection of RSS feeds just because there's ironically more of a democratic aspect -- anyone can start tweeting about whatever. They can go viral and disappear, they can gradually build an audience, etc. They can interact with followers or reply guys or stay aloof; they can recommend content and become a mini content aggregator in their own right. People can be anonymous or they can use their real world cachet to build a following.

Accomplishing the same thing via publishing an RSS feed is a daunting task -- you need to build an RSS feed somewhere, you can't interact with others or be easily boosted by bigger accounts to start to gain a following.

The "walled" aspect of this is basically the limitations of what the platform will allow, which especially under the Musk regime is a good balance of only very light touches of moderation.

People talk about the feed and the algorithm, but no two people have the same feed; the accounts you choose to follow will determine what your feed looks like, together with some generally popular content.