I think that's a naive statement, and it's also not really relevant to the original point being made, which is that existing mathematical notation can be difficult to grok.

Inventing new notation does not help with existing material - and that material is what makes mathematicians. People who can put up with old notation, especially if it is bad, are much more likely to become mathematicians: that gives a survivorship bias.

Besides which, you are welcome to invent your own notation, but good luck trying to get anyone to adopt it, particularly if the mathematical field involved is studied enough. Inertia is very strong, even in very abstract disciplines - aren't physicists still treating current as flowing the wrong direction?