Would a public option mean fewer claims denials?

Here I'm going to pose a question for which I don't yet have good answers.

One strong appeal of the public option in various Medicare expansion bills -- e.g.,  Medicare X, Choose Medicare, Medicare at 50, Medicare for America -- is access to an all-but-unlimited provider network (effectively eliminating balance billing as well as limited choice of provider). My question To what extent does a national public option also promise to strongly reduce the agony inflicted on patients by coverage denials? And secondarily, to what extent would minimizing denials weaken legitimate cost control?

Pieces of the puzzle are provided by studies of denial rates in various markets and public programs. These studies are based on partial or not-so-partial data sets and may be measuring different things. One question that's often unclear to me when reading them is how many or what kinds of denials directly affect patients, and which are eaten by providers or represent (or trigger) a de facto negotiation between provider and payer. Not to mention how many are justified...

With that caveat, a few data points:

A public option to get claims paid

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The top line in a new Kaiser Family Foundation analysis of claims data collected by CMS from insurers selling plans on HealthCare.gov is startling:

We find that, across issuers with complete data, 19% of in-network claims were denied by issuers in 2017, with denial rates for specific issuers varying significantly around this average, from less than 1% to more than 40%.

Caveats abound. Of 180 insurers selling plans on HealthCare.gov, only 130 submitted complete data enabling analysis by Kaiser.  The data does not include standardized "reason codes" and lumps together all denials, "including denials due to ineligibility, denials due to incorrect submission or billing, duplicate claims, and denials based on medical necessity." Most important, perhaps, there is no comparative data for employer-sponsored plans, which insure 15 times as many people as the marketplace (nor for off-exchange ACA-compliant plans).

There is, however, one useful point of comparison. Medicare Advantage plans deny 8% of claims, according to a September 2018 report from the Office of the Inspector General for HHS. That seems high in itself, but it's less than half the ACA marketplace rate, at least in the 39 HealthCare.gov states.