Hi, you are right. For basic applications of TOC with Kanban this is correct. In the early publications and Trainings of David Anderson you can see that he is openly referring to the TOC principles to achieve flow and continuous improvement. However, this simple visualization only helps to get a hunch on simple capacity constraints. It is important to recognize that those WIP limits not only should limit the WIP on the assumed constraint resource but also on the upstream “work centers” in order to not release new work to the delivery process.
Whenever you are dealing with constraints that are not as easy to spot (e.g. policy constraints) then the focus on WIP limits might just lead you to acknowledge that your throughput is limited but not why it is. Nevertheless this post was not supposed to emphasise this topic.