The TDX does not cover the entire 2500 mm^2 of the CPU but that's ok; the only important part is where the core is located, and a few millimeters around it. The core is roughly 10 by 12 mm, and is centered. Heatspreader or not, the same applies.
It might seem cheap for DangerDen to do this, but there's no real need for all that extra copper anyways, so if it cuts costs, it's all good.
