> Microsoft can't build a consumer OS with great power-management because the kernel also needs to work on high throughput servers?

Not only servers but they need the same kernel design to work well across a ton of different hardware/firmware combinations, form factors (Phone, Tablets, Laptops) and they do an OK job. But to excel they need to put in a lot more effort (working with OEMs, working with SoC makers is another challenge - everyone optimizes for Android now a days including Qualcomm and Nvidia). So yes, they can do it but it is exponentially more challenging for them due to their legacy and current market position.