I think it can be explained a little better.
When you write a post, you save it to your PDS. Think of it like writing a blog. You're done, you hit submit, it shows up on a server somewhere. You can run your own server with your own data, or use someone else's. That's exactly how a PDS works; it is a storage server for your data.
The AppView is a way to index all the PDSes registered across the whole network. If your server is crawlable by the AppView, all your data shows up in the app. This is like if your blog is crawlable by Google, you show up in search results.
When you like a post, you commit a "like" record to your personal server. When the AppView displays likes, it looks at every indexed PDS and shows every like it can find for that post (simplifying a little for clarity). Each one of those likes might live on different servers, some of which is self-hosted.
Because you can run your own PDS, you can commit any data you want to it. You can even commit things that services may find distasteful. However, the AppView may refuse to serve this content to users; this is how content can be removed from the network and how users can be banned. The federation equivalent would be defederation, except it happens to singular accounts rather than entire instances.
If you disagree with the moderation policies run by Bluesky the company, that's when you can look into running an alternative AppView. This is similar to disagreeing with the admin of a particular Mastodon instance and moving to a different instance. Of course, as mentioned running an AppView is much more expensive, but that hasn't stopped folks from trying (I believe Blacksky is trying to run their own AppView that is fully independent of Bluesky).
To use an alternate AppView, you'd simply go to a different website. This website will index PDSes the same way that Bluesky does, but it may index them in a different way and include/exclude different content. The data is still there (nobody can reach into your PDS on your server and delete your data), but the AppView admins choose which content they wish to serve to people using their community, just as Mastodon admins choose who to federate with.
In this sense, it is indeed truly federated. The primitives are simply different; it's more granular than Mastodon.
You can write your own content to your own server and let it get indexed to any number of AppViews; you completely control your personal data and nobody can reach in and delete that data randomly as they don't own it - you do (at the cost of ~$1/month or a Raspberry Pi).
When you use the Bluesky service, you are seeing their view of the network and what they choose to index. You may disagree with this view, just as you may disagree with the admins of Mastodon.social etc. In that case, you can choose to use another AppView (such as deer.social or Blacksky) that adopts different policies. Since account information isn't stored on the AppView and it simply handles indexing and moderation, moving between AppViews is painless and no data needs to be transferred from one server to another - you simply use a different bookmark.
It could be that you disagree with all the current AppView admins. You can host your own, it's just expensive ($300/month, as mentioned). You can also tailor your AppView to index less content, which will of course limit the amount of data you consume and give you a partial view of the network, effectively defederating you from anything you do not wish to index.
But there's nothing stopping you from doing so!