You might be forgetting that the Cell was released in 2006. The multi-core CPUs from Intel today are only just now starting to reach the peak theoretical performance than the Cell. Also, your Radeon was released when? 2009? Given Moore's law (which is still in effect for parallel architectures like Cell and GPUs), the factor by which your Radeon beats the Cell isn't too bad. Also note that the compute performance of an I/O device like a GPU can be limited by the I/O bus; both in terms of bandwidth and latency. GPUs used for computing typically perform best on large chunk, long running, computations. I believe that the Cell could possibly still trounce a modern GPU for smaller, less-memory intensive, jobs since it has access to main memory and is scheduled directly by the operating system (there's no GPU driver middle-man). This will change soon of course with on-chip integrated CPU/GPU solutions. However, it took nearly 5 years after Cell's release to get to that point.
So don't rag too much on Cell. It's very old, if not ancient, by microprocessor standards.