If it was that easy then everyone would do it. I call this the curse of the single number. There is this complicated machinery with lots of parts with different shapes, some are bigger some are smaller. However, the customer is not aware of the complexity and only sees a single number like 5W and maybe another number that showcases the performance score of the chip. Surely, since that is the only information we have about power consumption and performance it must be true in all situations. The reality is that those two numbers were measured during different situations and combining them into a meaningful calculation might actually not be possible.

For example. Geekbench measures peak performance of all cores at the same time and the power draw may go above 5W.

The 5W TDP may refer to normal day to day use where one or two cores are active at the same time for the duration of the user interaction (play a game for 5 min or something) and once the user stops using the phone it will quickly go back to a lower TDP.