The framing of "portability" is a bit confusing. Your data is not actually "transferring" anywhere, it's always in your PDS. These other apps and clients are just frontends that are displaying the data that is in your PDS. The data is public and open, though private data is in the works and hopefully will arrive in 2026.
This sounds like I need to host my PDS. Easy for me with no public profile but if I was someone famous wouldn't that mean I needed enterprise class hosting?
The data is not transferring, but the user is. When I sign up for e.g. Twitter, I don't want to sign up for Mastodon, or Bluesky, or Truth Social, or whatever other platform someone might create later. Thus I would not choose to put my data in a PDS. I feel like that would actually leave me with less ownership and control than I have now.
My point is that I don't believe the separation of frontend and data is desirable for a social network. I want to know that I am on a specific platform that gives me some degree of control and guarantee (to the extent that I trust that platform) over how my data is represented. I don't really have to worry that it's showing up in any number of other places that I didn't sign up for (technically I do since everything public can be scraped of course, but in practice there are safeguards that go out the window when you explicitly create something like a PDS).