This is my 2 cents, so take it with a grain of salt.
The Blade battery has the same drawbacks of other LFPs apart from one aspect. It is an iterative improvement in cell design to further address the safety issues of the battery packs via the reduction of heat buildup in the battery cells, which the LFP chemistry already addressed to a certain extent. The other benefits is like the cherry on top. But the blade battery doesn’t resolve the other fundamental issues of the LFP chemistry, and the major one being energy density. Thus I believe they went for weight savings in one area and more cells as the immediate solution to maximising the potential of their current LFP chemistry.
Also allow me to speculate a little, I have a feeling that the current blade battery is a stop gap to the solid state battery or other battery chemistries BYD is working on as seen in the patent filings in 2020 and Jan of 2021. Should the solid state or other chemistries pan out the current blade battery cells can be easily removed and replaced with the new cells at a later date, allowing for instant improvements without needing to fundamentally re-design their battery packs or their new BEV offerings as a whole.