It's generally true, isn't it? Otherwise we'd have ground breaking discoveries every day about some new and fastest way to do X.

The way I see it, mathematicians have been trying (and somewhat succeeding every 5~ years) to prove faster ways to do matrix multiplications since the 1970s. But this is only in theory.

If you want to implement the theory, you suddenly have many variables you need to take care of such as memory speed, cpu instructions, bit precision, etc. So in practice, an actual implementation of some theory likely have more room to improve. It is also likely that LLM's can help figure out how to write a more optimal implementation.