Interesting take. I would've divided the eras up very differently, though:

1998-2001: Pre-history. Urs Hoezle is the adult in the room. (Remember that Google was an engineering-driven organization early in its history; sales followed easily because they had a monopoly position on a critical portion of the Internet.) Culture is very much a scrappy startup, with everybody doing everything. Employees are young, idealistic, driven, and drawn to the company primarily by curiosity.

2001-2004: Consolidation in their primary market and experiments in others. Eric Schmidt is the adult in the room. The company is largely focused on milking the Search/AdWords cash cow and scaling at this point, but this was also the period where DejaNews, Blogger, and Keyhole were acquired, and Google Groups, Orkut, GMail, and Google Maps were developed internally. This was the era when all the incredible engineering talent was hired, because it was the dot-com bust when nobody else was hiring and everyone else was getting laid off, and Google was the only place doing really technically interesting stuff. Ended with the IPO, the launch of GMail and Maps, and the start of large-scale college hiring in 2005.

2005-2011: Diversification. This was the period where whatever Internet-based market you were in, you could bet that Google was developing a competitor or 4. Eric Schmidt was still the adult in the room. Company is very open and transparent internally, with lots of freedom to build your own pet projects. Teams are bigger with many more Nooglers because of the company's rapid growth (at least until 2009, when Google stopped hiring for 2 years). Focus is on exploiting all the great infrastructure and data that had been built. This era featured the launch or acquisition of Maps, Earth, Docs, Sheets, Presentations, Chat, Street View, Universal Search, Android, Chrome, Wave, Buzz, YouTube, and many other key properties. CFO changes in 2008, but there isn't a major change in culture until 2011.

2011-2014: Social era. Larry Page is the adult in the room. Google+ and Vic Gundotra wield outsize influence on the company, with company bonuses tied to the success of Google+ and Google+ having the ability to ask for integrations with any other property and get it. This was the time when the culture & brand started decaying - more project silos, more secrecy, more management by fiat rather than by consensus, and more decisions taken that damaged user trust or harmed the user experience for "strategic" reasons. Innovation is moved over to Google X, which often starved the product teams of their most innovative employees. Many large acquisitions, including Motorola and Nest. Hiring ramps back up, but most employees hired are typical big-company employees that are paid to do a job and not look around too much.

2015-present: Financial era. Sundar Pichai & Ruth Porat are the adults in the room. Company is restructured as Alphabet and Larry moves upstairs. Google itself is more focused on meeting its bottom-line targets, and is run more for efficiency than innovation. Also a focus on monetizing some of the Google X moonshots. Cloud becomes a big moneymaker, Google+ is shut down.

I'm curious - did you ever work for Google or were otherwise an insider? Your view is very much an outsider's perspective, focused on the CFO and big mergers rather than the culture, values, and projects. I was there from 2009-2014, and worked directly with people who were there from the Stanford days, and still have friends there. In my view there was a big culture change in 2011 when Larry became CEO, but the first half of the Pichette years (09-11) were culturally the same as the period that came before, just with fewer perks and less hiring because we were in the midst of the financial crisis. All of the milestones you cite from the Pichette years were actually post-2011, and IMHO are more a consequence of Larry taking over from Eric.