These are sound arguments. Medical devices have to be certified in all applicable jurisdictions and companies want to protect their competitive advantage. This is no different from, say, new drugs, which are similarly proprietary and the maker retains exclusivity for several years. Further, medications too are risky black-boxes towards end-users.

They are not sound in the context of human welfare.

We do not allow food companies to hide the ingredients of their products, because we know that companies (in the interest of profit) will fail to inform consumers about the dangers of eating unhealthily. Similarly, we do not allow meat producers to leave their meat ungraded because it endangers their "competitive advantage" - we understand (empirically) that doing so leads to food contamination and otherwise preventable disease.

Your choice of proprietary medicine as a counterexample is an interesting one. The pharmaceutical industry in the United States has a long history of "protecting its competitive advantage" at the cost of individual welfare - consider how frequently "reformulations" of the same base chemical are patented to continue milking a lucrative product that could improve the lives of thousands if genericized.

Perhaps even more pointedly, consider the fact that we deem it acceptable (and necessary) that the FDA step in and regulate the release of new drugs. Is there a valuable distinction to be drawn between the sort of regulation and evaluation that the FDA does and the sort that would be possible if programmers could openly evaluate medical devices?

Your argument that opening up the source code might have prevented her death is facetious.

Facetious?

You're attempting to justify the release of a (potentially fatally) flawed product on the grounds of lost "competitive advantage".

If you lost a family member to a faulty (yet certified!) medical device, would you feel that their death is justified by a marginal improvement to some company's bottom line? What if it wasn't a medical device with closed code, but a miracle pill whose manufacturer refused to release the formula to the government for analysis?

The argument I made in my original comment does not rely on the (un)soundness of your original claims - it is a moral argument about the value we place on human life. I'd be willing to bet that, even if you think that closed source is superior in every fashion, you would never be satisfied by your own justifications in the case of a personal tragedy. This contradiction suggests that, at the very least, we must draw a distinction between justifiably and unjustifiably closed source code.