I think you definitely want to structure the topics more. Even if he continues on worksheets they presumably could be sequenced rationally. Have you tried comprehensively tracking the topics over time to make sure your impression is correct or alternatively just asking the teacher how she is choosing them?

Also Khan academy can be just as random topic-wise. Imposing some hard ordering on its units definitely improves the experience not that I personally would want that to be the primary instructional
mechanism.