Those metrics would only be meaningful if the average visitor knew how fast websites and computers can be, and if there are well-known alternatives to your site. Having standards is preferrable to aiming for mediocrity imho.
YouTube probably has decent retention rates but it's a bloated pile of UX hell that people use for a lack of alternatives. Maybe that's why Google manages to make it even worse over time without realising they're digging a second Mariana trench of quality.
Of course visitors don't care about commercial and marketing metrics.
They clearly rely on other metrics to decide whether or not visit or stay on a site. And my question still stands: who has numbers or data that show that those 14kb pages perform better in regard to the commercial metrics than heavier pages ? And I mean in the field data, not a synthetic test.
A trivial search will find you tons of heavily reviewed research that shows web page performance directly impacts e-commerce conversion/sales and this is widely known in the industry. This article laid out a solid technical explanation for why staying under 14kb can have substantial improvements in performance. You refusing to see the connection there, or are you disputing it?
edit: No, it's not. It deals with TCP window but in no way does it deal with customers conversion, retention rates and all those things.