As someone who went through that era and worked on a cross-platform title. The issue wasn't that the PS3 was heterogeneous, it was that the X360 came first so

As someone who went through that era and worked on a cross-platform title. The issue wasn't that the PS3 was heterogeneous, it was that the X360 came first so everyone wrote for a system that had relaxed memory constraints. When the PS3 came along all of a sudden things that weren't vectorized didn't run slow, they just flat out didn't run at all. Fun fact, the few engines that were developed for the PS3 first and X360 second ran circles around everyone else because all the vectorization work for PS3 meant they fit in caches really nicely and had zero cache misses. Easily 2-4x faster than titles doing equivalent work.