So BASB also has a second part, which is capturing and progressive summarization. I haven’t taken the course so I’ve only read blog posts about it, but the name is fairly suggestive of what it is.
IMO “progressive summarization” is not as good a method of knowledge creation, especially for original, creative work, compared to Zettelkasten. Presumably, one’s hope is that the later layers of summarization would be more synthesis than summary. Zettelkasten seems more explicit in that respect.
If you delegate content of the work and management of thoughts and information to the method described by Ahrens, then the part that PARA that matters is “PA” like others have said. PA by itself is just GTD with some grouping, which I think one will probably do anyway.