That's not entirely accurate. Yes, MS has designed its own laptop, but the fact is that windows isn't specifically customized to run that hardware and only that hardware so it can be optimized. Its still needs to run a wide gamut of new and old hardware and given the complexity and varied nature of what hardware it can and does run, its pretty amazing.
As for the M1, I don't own one, but seeing the ARM forum, its a solid computer. At a time when Apple announced its transition from Intel to ARM, they needed to show the world that they can produce a capable processor. They not only showed the world a capable processor, but stunned the industry with a blazingly fast processor that stretches battery life to inconceivable time spans.
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I'm truly impressed with the M1 Macs, while the platform is not the best fit for my needs, and wants, that doesn't mean I'll bad mouth it. I think they're a great machine and I can't wait to see what Apple does for the 16" MBP.