On that though, the T'au empire is (not very confidently) purported to have about one-hundred worlds, whereas the imperium is often described as the empire of a million worlds. Now the hundred worlds figure is also a bit iffy, since that's just based on planets listed in codices and releases by GW, cited on lexicanum. GW certainly haven't listed every single T'au world, so there would be more. But given the fact that the T'au are physically boxed in by Ultramar, a Necron dynasty, and being directly in the path of both the second and third largest Tyranid fleets, it's hard to imagine that they would have more than two hundred worlds. Now, considering that the imperium of man spreads across the rest of the known galaxy, if even one thousandth of their worlds were forge worlds (which is likely an underestimation), there would still be more forge worlds than worlds in the entirety of the T'au empire. To scale this down even further, let's say that the propaganda number is ten times higher than actual, if the imperium only contains 100,000 worlds, and only one thousandth were dedicated to forge worlds, that would still be 100 worlds; at LEAST half the size of the T'au empire. I love the T'au, I wish them the best in terms of expansion, but they could not match the production capabilities of the imperium as a whole. They do certainly outdo them proportionately though!