If you're going to characterize "one-trick ponies", you either need to read the whole thing anyway, or quote and take issue with specific parts for long enough so you've demonstrated the trend convincingly.

The strategy of not reading (all of) something and then making sweeping generalizations leaves a lot to be desired.

You also need to argue why a one-trick-pony can't be an origin story (myth--which you've already agreed needn't be true). After all, the "America, the Land of the Free and Home of the Brave" origin story is pretty one-trick-pony-like (and not particularly accurate).

You do make a reasonable case for why it's an origin story that you don't like, but it would requires a lot more careful argumentation to demonstrate that it is fundamentally too biased or incomplete to be usable. People who still suffer from explicit or implicit racism may like very different things from you, after all, and there's no particular reason to presume that your preferences should supersede theirs.

Or you could argue why it's an origin story which is harmful, which you started to do, but that also requires a lot more. In particular, you might be able to make a strong case that the founding principles of the United States set the stage for all the progress in human rights thereafter, even despite all the personal interests in doing otherwise, and that the 1619 version lacks a similarly compelling principle to organize the improvement of society. Perhaps some other approach may also work. But it requires something more--you have to lay out the alternatives in more depth to be able to convince others of which is superior.