That paragraph is incorrect. SPF/DKIM is not about reputation. The main purpose is preventing domain impersonation from unauthorized senders. E.g. mail servers will reject fake emails from "upofadown@microsoft.com" because you don't control any email servers that's whitelisted in microsoft.com DNS TXT records.
E.g. I was able to register a brand new .com address and then successfully send to gmail and MS Outlook accounts within minutes because I had proper SPF/DKIM in the DNS records for that new domain. That new domain had zero reputation and yet Gmail accepted it because SPF/DKIM was configured correctly -- and -- the underlying ip address of the server it came from had a good reputation.
If SPF/DKIM was truly about "reputation", it would mean I'd have to wait days or months for reputation history to build up before Gmail accepted it.