Is Overbreadth the new Promise Doctrine?

I have a new draft paper available on SSRN, “Overbreadth in Canadian Patent Law.” Here is the abstract

Under the overbreadth doctrine, a claim that exceeds the scope of the invention disclosed in the specification is invalid. While the doctrine is well established, it is redundant in the great majority of cases in which it is invoked, as an overbroad claim typically encompasses subject-matter which is not new, lacks utility, or is obvious. When overbreadth is not redundant, a puzzle arises: what is the principled justification for striking down a claim to an invention which is in fact new, useful, non-obvious and sufficiently disclosed? In such a case, how can it be said that the claim is broader than the invention? This article argues that overbreadth properly arises as an independent ground of invalidity in the context of the “roads to Brighton” problem, in which the question is whether the first inventor to achieve a result known to be desirable may claim the result itself or may claim only their particular method of achieving it, but the answer to this question is controversial. Overbreadth was also applied as a truly independent ground of invalidity by the Federal Court of Appeal in Amfac Foods Inc v Irving Pulp & Paper, Ltd. This article argues that Amfac was wrongly decided, both on its facts, and in its approach to overbreadth. The article warns that the Amfac approach, if widely adopted, risks invalidating patents for inventions which are new, useful and non-obvious, on the basis of an arbitrary parsing of the disclosure, in a manner reminiscent of the promise doctrine.