I think it helps to have both the sorts there, because it gives the students another opportunity to solidify their understanding of algorithms and because they are indeed expected in things like AP CS. Personally, I find them different enough that I need to spend time on each of them to grasp them- I always have to draw algorithms out when I'm learning them, so it helped me that we had the different diagrams and visualizations for each one.
When making KA content, we have to think both about the student that's going through the content from top to bottom and the student that's "snacking" on the content, like finding it via Google search. So if you knew that a student was going to do the whole thing, you could do more just-in-time teaching - but if you didn't know, then it'd be doing a disservice to the snacker to leave out something like Big O notation, because it'd sure be strange if someone learned Theta and Omega and came away not knowing that last one existed. We did spend a while restructuring asymptotic notation in particular, that was one of the topics we debated different approaches to.
We also debated the use cases for recursion, and if we should include the classic factorial challenge. We went for it in the end, as you saw. I think recursive art is my favorite, and works well in our ProcessingJS environment, but one could argue if that's real world :-) I believe that Devin is working on another tutorial with recursion and specifically on how students can come up with their own recursive algorithm. I'll suggest the looking through directory example to him.
Yep, we are working on a quick sort visualization. I am also quite a visual learner.
The neat thing about online curriculum is that we can get feedback from all the students that use it and improve it over time. We'll probably look at all the feedback in a few months, once it's been out there for a bit, see where the dropoff points are, see what the common questions are, and use that to decide what needs changing.