Thank you for referencing TSAnalysis.jl.
I think you highlighted some interesting points. My view is the following.
For what concerns the time-series field the number of registered packages compatible with Julia 1 and with unit testing is rather small (a subset of the above).
I am toward the end of my doctorate (one year and a half left 
) and my research is mostly on time series. TSAnalysis.jl is still preliminary, but I will consistently add new features (see this link for more details). I plan to cooperate with other developers (co-authors and externals) and I am trying to avoid overlaps whenever possible. However I also want to have control on the most primitive part of my package. It might be a personal limitation, but I aim to:
- have enough security to be confident in using TSAnalysis.jl as a basis to write academic papers;
- define a solid and modular layout that allows for regular updates.
I suspect that different mantainers might have similar perspectives. Of course, this might create overlaps. That said, users generally tend to concentrate around the most efficient and friendly packages. Git often pushes the most used.