I also think you might be a little over-enthusiastic if you were suggesting that the reverse engineering jobs being undertaken will rival source code access. Just consider the amount of work produced per unit time by the FOSS world vs. the "useful" work being achieved by the underground or by the research world focused on Windows. Clearly one type of work is much more difficult (ie, the one without source code access).
You have high esteem for the top researchers but perhaps miss out on the value and contributions from those not known in the industry. Not to drag SELinux back into this, but a bug fix can have many repercussions, including fixing security issues in the making (not yet analyzed by black hats or even by expert white hats because of information overload). Many people work on their concept of correctness and don't stop to categorize something as security related.
Remember that it takes much more time to develop an exploit usually than it does to fix the bug. With two competent parties analyzing code, which is more likely to finish first, on average?
In fact, you get something of a race to reporting bugs in the FOSS world (to at least get credit) because it is so much quicker to do this than to build an exploit. In the closed source world, you have lots of time to build the exploit with much time left over to craft a business plan around the series of exploits you will build.
Also, the number of eyeballs matters. There is a reason FOSS is quick to fix problems and many times anticipates them, one way or the other.
Of course, if the reverse engineers had done their jobs (assuming it was easy), then they would be patching Microsoft's software for Microsoft just as quickly as is done for FOSS. [I was being facetious.]
You mentioned all the work being done for Windows. Well, I think as time approaches infinity, we see people moving off Windows and onto the more transparent Linux. Research advances more when you have access to the most information possible and then try to fill in those fewest number of remaining holes. This obvious conclusion is among many not escaping those slowly but surely moving to support and contribute to FOSS.
Mainly with Microsoft software in mind, I say that you don't need to (eg) overflow a stack to subvert security or disrupt privacy. You can do it right under people's noses, and it is difficult to catch this because nothing unordinary is happening among an ocean of more unordinary stuff flashing by at hundreds of millions of ordinary instructions per second or faster.
In short, I am not going to be convinced that the reverse engineering job is keeping a check on Microsoft no matter how many tools you mention, nor am I going to be convinced that reverse engineering is comparable to having source. It's one thing to find flaws (diff to help you out, etc). It's another to verify things are correct or are not misbehaving in places you haven't looked. Finding a gem vs accounting for everything in the land. [And surely, the tools don't get as much information as source code+binaries]
To belabor the point.. RE leads to much more information overload. You filter out much to focus on things of interest. If 80MB source patch for Linux is tough to follow.. if everyone is trusting everyone else to see source as you stated.. then how much more difficult is the case when you don't have source yet have lots of changes in binaries. Remember that binaries are updated while the system is running with no need to announce what is going on. The system software can piggyback on any network conversation in any way it wants. It's too large a space to track which is why just looking at the network is not enough, and the binaries clearly have not been deciphered completely. Spotting problems in diffs is much easier than understanding the base. How well does the research community know the Windows base? I don't think nearly well enough. [Eg, you invoke things that Microsoft themselves have stated about their products rather than pointing to an analysis of their binaries to actually show/prove X or Y property is there. With sarcasm.. Don't the reverse engineers know all about Microsoft products the way we know about Linux? Why can't we point out where Microsoft does this or that in actuality (not in theory nor in their marketing nor in their purposely scrapped projects), as we can for Linux, but instead rely on their cribnotes to the public? What kind of checks are those? Who cares that these dissembling tools have progressed "hugely" recently?]
As concerns Red Hat being a public corp just like Microsoft, I addressed that already by saying that the issue is about checks and balances (we look towards their businesses for that.. one relies on openness the other on closedness) and additionally that Microsoft has monopoly profits to protect.