Cameras have low processing power because they don't require all that much. The issue is the physics of light severely limiting what a sensor small enough to fit in a smartphone can do. A small sensor requires either fewer pixels, smaller pixels, or both.
Fewer pixels = lower resolution = worse image quality.
Smaller pixels = less light gathered = worse image quality and far worse low light performance.
While something like this could be made, it would be very expensive, and there is no possible way it could come close to the image quality of even an entry-level DSLR or mirrorless camera. Even the best lens in the world can't make up for a bad sensor. Smartphones can use their higher processing power to try to hide it with HDR and absurdly bad faked depth of field, but it will always look noticeably worse compared to the same photo taken on even a very old, low-end APS-C or full frame camera.
Smartphone cameras definitely fill a big niche in photography, but unless there's an incredible breakthrough in sensor technology, their physical limitations will always prevent them from being good enough for widespread professional use.