It's not that the idea of an opinion poll isn't important, it's that they simply don't work. Even when the poll isn't sponsored by a partisan organization (in which case the poll will come out however the pollsters want it to), issues polling is plagued with biases; it's very difficult to design questions whose polled answers generate any insight.

Candidate polling is at least tied to a single concrete action that the respondent will actually take. It's not great, but you can learn stuff from it.