I find your assertion only partially valid and in the interest of provoking insight on this topic, I will state my argument.
I will assert that the number of backlinks is unimportant while the collective “strength” of your backlinks is all that matters regarding this as a factor in ranking SERPs. If you have only one or two really great backlinks you can easily outrank pages with hundreds or even thousands of backlinks. This is obvious by simply observing the SERPs.
So this begs the question “what is meant by strength”?
The word “strength” is a relative term, so it is completely ambiguous without providing context. What makes one backlink stronger than another? Is it PageRank? Clearly PageRank is not the deciding factor all on its own, if it were we would see SERPs sorted roughly by PR.
It seems clear to me that search engines sort their results based on relevance and sub-sorts pages with equal relevance on other factors often referred to as “Authority” and “Importance”. Assuming this is true we should focus first and foremost on factors that influence relevance.
Backlinks clearly influence SERP ranking, but only when there is some relevance present in either the anchor text or other on-page relevance factors.
What is less clear to me is exactly how backlinks influence relevance. It appears that the relevance of anchor text plays a strong role, but what about other factors? The PR of an IBL seems to be a factor. I have seen data that “suggests” this is true, but how do we isolate the cause from the effect? Perhaps the key factors that influence the “strength” of a backlink are more prevalent on pages that have higher PR. I haven’t seen much data or heard of testing done to isolate the cause from the effect.
In my own experience, I have seen anecdotal evidence that suggests that the PR and anchor text of your backlinks alone may not make up the complete formula in determining the strength of your backlinks.
If anyone has done any testing to isolate the factors that influence the relative strength of a backlink I would love to review the data and testing methods.