I know that some writers work best if they approach writing in a systematic way (I'm one of them). If the Jarvis Method gives you a base to work from, so you can develop your own method, then go for it. But I still think your goal should be to develop your own method.
The reason why people complain about "formula" fiction is not so much that people write to a rule, but that so many people write to the same rule, and the fiction they produce is all a bit samey. So you should look to change the method and add to it to suit yourself. Otherwise, it's not really you -- only a paint by numbers replication of someone else's work. And if it's not you, well, what would be the point of writing at all?