The bigger issue is they're saying they're decreasing support as of this year. Even if we ignore the fact that Russia will bomb those factories, factories don't just pop up magically. Often taking years to build in the first place. If the support dries up as of this year, there's no way Ukraine would be able to switch to domestic production.

Essentially what's really being said is Ukraine will be stuck in a stalemate at best for this year and domestic production might support Ukraine enough for future years assuming there are no delays to factory creation. But just look at the chips act to see how well factory creation goes.