·Verizon Online DSL
I never said it wasn't. In fact, off the top of my head I know that the capacity of one PON is 2.488 Gbps down, 1.244 Gbps up (OC-48 down, OC-24 up). This is how Chattanooga EPB is able to deliver symmetric gigabit service over GPON...it's a little bit of a squeeze to do that, but nothing nearly as shaky as Cablevision's habit of shoving 101/15 onto 3x1 bonded DOCSIS 3 channels, or 30/5 onto a single channel up and down a few years back.
I merely suggested that Verizon's 300M tier was placed just out of reach of Comcast's current network capacity at the last mile, so VZ won't have to upgrade its tier speeds until Comcast starts handing out 24-channel-bonded modems to its highest-end subscribers. Those modems are out now, but in order to use them Comcast would have to dedicate 144MHz of their cable network to downstream DOCSIS channels, out of maybe 800MHz available for downstream communications overall (860MHz total, minus below-the-split return path channels). At that point Comcast will be able to hit 300 Mbps without an issue, but that level of plant upgrades would take a year or so to complete across any significant portion of their network, leaving Verizon with a bunch of well-paying, friend-recommending power users once again.