What is DDS?
DDS is DirectDraw Surface, the texture format games ship. Its point is that the GPU reads the compressed blocks directly, so BC1/BC3 textures never need unpacking at runtime. FileSorcery reads it and converts out; writing good block compression is a job for a dedicated compressor.
What is WEBP?
WebP is Google's image format for the web, and the rare one that does both jobs: lossy compression that beats JPEG at the same quality, lossless compression that beats PNG, and an alpha channel either way. Every current browser reads it; older software often still does not.