I don´t think so. At first, not every Distro has a large team behind that is able to fix security issues in time or at all . That means that most Distros are insecure in mass utilization. Second, "the lack of attacks" on Linux systems will leave a lot of security holes undiscovered. That is making the system insecure. Luckily, for the same reason, it doesn´t need this security.
However, Ubuntu developers accuse Mint of excluding important updates:
Ubuntu Developers Say Linux Mint is Insecure. Are They Right
There is another thing. The City of Munich examines the re-introduction of Windows as Server downtimes are too long and employees "suffer".
Verwaltungs-PCs Stadt M nchen will von Linux zur ck zu Microsoft - DIE WELT
LiMux Neuer Wirbel um Linux in M nchen heise open
I can't argue that the "scatteredness" of Linux is a problem. Always has been. And yes, if the 100's of small *nix OS's were at the brunt of hackers and script kiddies they would melt with ease.
Having said that, it is changing. Ubuntu and Mint are slowly making others obsolete outside of the server world. I hope it continues.
A truly commercial, branded Linux is needed. RedHat is a good example of a successful commercial Linux brand.
Windows has it's strengths. Like I said earlier, I consider Windows 2000 one of the best OS's made. As well as server 2000, infinitely better than NT Server. I hated NT Server.
Embedded application servers, I can't complain. We have embedded systems that have been running 24 hours a day for years.
My issue with M$ is an old one. You have heard me say it before, no sense rehashing it again.