You started mentioning Microsoft's occasional slowness when fixing bugs, but it's irrelevant for non-Microsoft software? Interesting.
The thing with most of the "Microsoft Security Bugs" is that they usually allow an intruder to enter your PC and "own it" if you will, how many people "owned" computers through this "non Microsoft bug"? It also exasperates the problem that M$ operating systems have a majority market share which increases the attack visibility (where as this is not so much of an issue for Xorg).
What would be the priority in a busy hospital? And where would those priorities lie?
"I pricked my finger and need a bandaid" ~ Xorg
"Someone cut my arm off... HALP" ~ M$
While i'd love to live in a world where bugs don't exist and everyone lives in "Happy Fantasy Land", this is not the case and priorities are needed some times.
There's no such thing as "secure enough" in the post-Snowden era.