The fact that anyone at Google wrote this memo tells you more about Google than it does about AI (or anything).
What’s the moat for Apple (after all, they’re all phones and computers)?
What’s the moat for Microsoft (after all Google and insert thousands of other competitors offer docs, sheets, etc)?
What’s the moat for Facebook (after all, it’s just a social network)?
What’s the moat for Google search (it’s just another search box)?
The moat isn’t the product, it’s the business. Every one of these companies built a business that served customers well (people who want the best phone, company IT departments, advertisers, and advertisers again). The moat is a business so good at serving its customers that you can afford to offer a better/cheaper/faster product than others because you serve a well paying customer the best. Done well, your moat is then the momentum of being the default option.