Much much more to how neural circuits work than just connectivity. Good example to keep in mind is C elegans (https://en.wikipedia.org/wiki/Caenorhabditis_elegans). Despite knowing the connectivity of its 302 neurons, and the whole organism consists of just a few times that many cells, AFAIK we still don't fully understand how its nervous system works, e.g., how it makes decisions etc.

(There is a lot of work on this organism, and I haven't kept up with the literature. So maybe the comment is a bit out of date... someone more knowledgeble should chime in.)