Xfinity and AT&T Fiber do /not/ use PPPoE. Xfinity is built on DOCSIS, and AT&T Fiber is built on XGSPON. This means neither one relies on PPPoE at the data link layer. XGSPON uses XGEM/XGTC at data link layer, DOCSIS uses MAC (same data link protocol as Ethernet).
This article is making a bunch of assertions which are just patently false. PPPoE is basically old hat at this point. It's extremely high overhead anyway, so is only used for DSL because DSL is an old approach.