I would submit that's hypothesis is incorrect – Polyamory is not about creating a selection buffet for the physically attractive, but rather de-emphasizing specific traits as part of the attraction equation.
Put another way, if you don't need to permanently handcuff yourself to a single mate for life, or serially pursue theoretically-good single matches in turn over time, you are instead freed to selectively or massively experiment with/iterate across multiple coincident relationships based solely on the parts of such relationships that bring you joy… And then, ideally, "fill the gaps" as necessary with additional "fitting" relationships.
Polyamory is about "getting a wider spectrum of desires more consistently fulfilled than is statistically likely via monogamy", not "catching all the hottie-type Pokémon".
In the studies I've seen, and the polyamorous individuals I've interviewed, the inequalities of specific polyamorous couplings are far more centered around individuals' disparities of time, attention level and tactical/strategic intent for the relationship, rather than looks and money. Do more attractive but vain polyamorous people seem to have an easier time finding attractive compatible partners? Maaaaaaaybe!
Another point to remember: neither monogamous nor polyamorous relationships, by definition, presume eventual marriage (which seems to also be an undercurrent of the majority of answers here). It's much more likely, instead, that widespread societal polyamory would simply make romantic relations a more continuous/integrated part of the I LIKE YOU curve, rather than a jarring state change to an entirely different, if seemingly-parallel I LIKE-LIKE YOU graph.
Having said all that, the answer remains, of course, NO. Simply adding the ability to offset gender ratios with multiple partner relationships would not de facto guarantee proper equilibrium across the combination of gender, sexual identity, and sexual preference… And, in seriousness, it's never about the ratio, anyway. Every relationship that doesn't happen, doesn't happen for its own reasons.