As COO, Tim was responsible for reorganising Apple's supply chain. Before him, Apple had awful execution and would regularly overproduce some models that would

As COO, Tim was responsible for reorganising Apple's supply chain. Before him, Apple had awful execution and would regularly overproduce some models that would end up unsaleable, while having shortages of other models. I'm pretty sure this was a substantial factor of the operating losses of the 1990s. Under Tim, this changed radically. Initially Apple solved the problem by drastically reducing the number of different models, but by the time the company managed to produce iMacs in 5 different colours without noticeable misproduction of numbers, it was evident that it it had become much better at execution. And around that time, Apple also started turning a profit again. So I'd argue that Tim may have been one of the key drivers of Apple's profitability. I'm not sure how much value he added over a hypothetical replacement level COO, but empirically, he was an enormous improvement over his predecessors.