The latter is my theory about music notation; that inertia is not even at issue yet because there are no serious alternatives.
And inertia might never be an issue, because music notation is a fluidly changing system. TCP and qwerty/Dvorak are static systems that don't ever change, so you can argue about which one's better. Music notation is changing and improving, so it's hard to suggest that people are resisting change, and hard to suggest that something better will supplant it, right?
I agree with your theory in general though, outside of the issue of music notation, and I think a lot of people do. It's just a matter of finding the right examples that clearly demonstrate it. And it would be really interesting to somehow quantify the amount that something needs to be better before people will adopt it. It's like static friction in physics -- it takes more force to get something started moving than it does to keep it moving.
"the best-documented experiments, as well as recent ergonomic studies, suggest little or no advantage for the Dvorak keyboard."
https://en.wikipedia.org/wiki/Dvorak_Simplified_Keyboard#Con...
"The trap constituted by an obsolete standard may be quite fragile. Because real-world situations present opportunities for agents to profit from changing to a superior standard, we cannot simply rely on an abstract model to conclude that an inferior standard has persisted. Such a claim demands empirical examination."
http://www.utdallas.edu/~liebowit/keys1.html
Musical notation is a vastly more complex system than keyboard layout, and I don't believe we have a Dvorak of music notation to even compare with. There are no contenders for musical notation that a large group of people believe are superior. So there's no reason to believe that inertia is keeping people from using another notation.
To go one step further, music notation is constantly changing, it has been evolving, adopting and incorporating the best ideas for thousands of years. What reason is there to not start with the assumption that it already took the best changes so far? I have no doubt that if superior ideas for notation develop in the next hundred years, that at the end of it, we'll still call the result 'standard music notation'.