He has lead Apple after Jobs died which is no small task. He oversaw the iPhone market which has been growing continuously under his leadership. He started and grew Apple’s services division, launched Apple Watch, AirPods and the Apple Silicon transition which have all been massively successful by any metric. I don’t understand how Tim Cook’s tenure can be considered not impactful.
I think the metric that matters is delta vs a hypothetical other CEO. It's really really hard for me to imagine Apple flubbing a launch of headphones or earbuds. I think that's why AirPods are less impressive, even though they've been a wonderful success and a great product.