As critical theories are self-critical only in accepting critiques from critical theories (all other criticism is deemed an application of hegemonic power), it is not possible to defeat a critical theory with matters of facts. They can only be problematized more severely, which, while it defeats the specific critical theory, ultimately replaces it with a stronger critical theory. The most obvious way to undermine the 1619 Project in specific, then, is not to argue about matters of historical fact around the events of 1619, 1776, 1863, or any such period; it’s to point out that it erases the earlier and more severe suffering of American indigenous people who were genuinely enslaved and subjected to genocide by the Spanish starting almost a century earlier.
Again, it is not the matter of fact here that will overturn the 1619 Project (as being, itself, problematic). It is specifically that the 1619 Project did harm to indigenous peoples by erasing their allegedly earlier and more consequential suffering (Again, because it’s so difficult to remember about critical theories, truth and falsity do not matter in these analyses; it just has to be forwarded forcefully enough while appealing to the lived experience of suffering of subjugated indigenous people).
Critical theory projects like the 1619 project is therefore not a tool to improve our historical understanding, and is inherently in conflict with the liberal projects ways of finding truth.