I wasn't considering anything, let alone 'making an argument'. Anyone who listens to non-specialists like me to determine security strategy is asking for trouble.
I also wasn't making any comment about 'banking on difficulty of exploit', what I was asking for was relative risk. I think that all code is exploitable. The question I had was, is the exploitation of a particular UAF bug sufficiently easy that it outweighs the base risk of a new exploit being found. If I have finite resources, understanding where to apply them to improve risk is important.
The other responses have answered my question in some detail.
I'm sorry, my tone was not intended as "what are you even talking about!?!". My tone is intended to convey that security penetration skills have become scarily good and "is it theoretical?" is almost no longer a question worth asking, because the skills, techniques, and tools to take what superficially seems to be a hairline crack into full-blown network ownership are unbelievably well developed.
As I said, I am on the defense side myself, and I will freely admit I can get a bit tetchy when doubt of the viability of a vulnerability occurs; I frequently find myself in the position of being a "team captain" trying to explain that, no, seriously y'all, the other team is coming to play, they've been working out, they take illegal steroids, they practice six days a week, they don't play by the rules and they're coming for our scalps and you're on your third beer telling each other how easy this is going to be... it's not exactly game-winning prep you're doing here....
The author was able to take an off by one error which allowed writing a single null byte all the way to full code execution. These guys are unbelievably good at what they do, and as you state, you can pretty much assume that any vulnerability is exploitable with sufficient effort and skill.
I also wasn't making any comment about 'banking on difficulty of exploit', what I was asking for was relative risk. I think that all code is exploitable. The question I had was, is the exploitation of a particular UAF bug sufficiently easy that it outweighs the base risk of a new exploit being found. If I have finite resources, understanding where to apply them to improve risk is important.
The other responses have answered my question in some detail.