2) Extrapolated averages on incomplete data are certainly suspect, they are meant to be taken with a grain of salt and are most applicable to people in the affected industries for them to validate against their own data. FWIW The highest percentage of malicious, automated traffic that I've seen has been 99% which, yes, is crazy and should sound unbelievable.
3) Noted, definitely. It is certainly a tough number to nail down because it is very dependent on all the things you mention. I trust our data because we've been at this the longest, were the earliest, and we see a lot of the unadulterated attack traffic that has gotten through many existing defenses so we see the stark difference on day one.
Disclaimer: I contributed to the report in question (but was not consulted or related to the posted article)