The same doesn’t appear to be the case with ‘Mastodon’. It’s home page is user friendly and Mastodon itself is fairly user friendly. Some of the servers already have several thousand of users.
I am registered on several decentralized web platforms, but nobody else in my family is registered on anything other than the usual suspects, Facebook, Twitter, etc. That means, as a parent, grand-parent and great-grand-parent, if I want to keep track of all my fairly scattered family, I have to use the same platforms too. The more they use them, the more dis-inclined they will be to ever leave them.
This brings me back to the original question. If Mastodon is already established and continues to gain traction, and if WebID’s are not compatible,
then solid, despite being far superior, may not be the platform of choice. IMHO speedy development of Solid is as necessary as excellent development of Solid.