"Microsoft for several years has been dismissive of Chromebooks, going so far as to run ads attacking the devices, from late 2012 into early 2015"
If you run ads criticizing a competing product then it's pretty obvious that you are frightened of it. Why else would you spend money belittling that product?
If you do it for the years then that means that, not only are you scared, but you aren't able to come up with something to complete.
If you then launch something to compete it proves you think your competitor was right all along.
The thing that gets me though is that where Google built something intentionally small and light to keep hardware costs down, it looks like Microsoft is launching a cut down version of Windows. Cutting down bloatware will never produce as lightweight a product as building for lightness in the first place. Ask Colin Chapman.