Even if I accept your interpretation, it still doesn't justify the description "you're not the user, you're the product" In the case of the private highway example, even if the customers are the advertisers, the
product being sold isn't the drivers, it's the billboard space.
Google's users are not its products. You might claim its users are not its customers (users != customers), but that does not imply the users ARE the products. Just like the New York Times readers are not the real business customers, the advertisers are, however no one has ever exclaimed "The New York Times Readers are the Products!"
The Product is the New York Times, because that is the thing _Being Produced_. It is the work product of the journalists.
Likewise, the work product of the engineers, SREs, PMs, managers, ops and support for Gmail is the Gmail Service. That is what is created out of the hours they put in. There is an ancillary product that leverages externalities produced those products (virtual real estate to auction off), but it is not people's data as the product being sold.
This meme is really tiresome because it doesn't get to the root of the matter, which is, are the incentives of those working on Google's products aligned with the incentives of the business operations which have to derive a return on those investments.
There are two ways to look at this depending on your level of cynicism:
1. Google is a smart company that looks at the long term and realizes value by the creation of positive externalities. That is, it works from the premise that if you make good products that please your users, you will retain and get more of them, and there will be opportunities to monetize that. That is, retaining users is paramount, ergo, user trust, branding, and generally not pissing off users is very important.
2. Google is a short sighted company that looks at what is currently has, lets bean counters manipulate its products purely to increase the bottom line by maximizing the amount of stuff they can sell. This means, they only consider the wishes of advertisers, and act to increase purely the amount of ads that can be shown, regardless of how much it annoys users.
Now, you can decide to believe #2 or #1 depending on how harshly you view the trajectory of Google products over the years. To be sure, they have done things that have annoyed users. But I believe, based on evidence of actually working here, that the primary impetus of engineers and product managers who guard the high level product features, that the focus is tipped towards user concerns.