Cell was very advanced and way ahead of its time for the parallelism and SIMD capabilities.
The issue was learning how to use it to extract the full theoretical power out of it.
That was done in the second half of the PS3 generation by Sony's top studios and some top third party developers and the results were unmatched.
But other studios just didn't have the time or incentive to do that kind of research.
That generation proved that ease of development was way more important than peak power.
There was also the issue that Cell was used to cover some of the weaknesses of the RSX and do some graphical tasks in its place while with a more competent GPU it could have been used for physics, procedural content generation and other more interesting stuff.
I don't remember if the Cell based GPU that Sony wanted to use before going with nVidia had some if its specs leaked.
Certainly it would have been a nightmare with developers struggling to implement even the most basic graphical functions and zero standardization for multiplatform publishers
even if the RSX was not as powerful as expected it probably saved the console in terms of development tools and standardized development.