Whats the real-world impact of motor placement on e-bike performance, specifically when comparing hub-drive and mid-drive systems, and can we move beyond the conventional wisdom that mid-drive is inherently superior due to its supposed efficiency advantages, considering that modern hub-drive systems have made significant strides in reducing weight and increasing torque output, and also taking into account the added complexity and potential reliability issues that can come with mid-drive systems, which may offset any theoretical efficiency gains, and are there any notable examples of e-bikes that have successfully utilized hub-drive systems to achieve high levels of performance and efficiency, and what role do factors such as battery placement, gearing, and frame design play in determining the overall performance and efficiency of an e-bike, regardless of motor placement.