I personally don't think there would ever be an issue with this install. But you are trying to avoid any differences between the paths. If you have a smaller pipe you would have a change in heat disipation and inductance for example, which might result in one path taking a larger amount of current.
I thinbk that cite came from a discussion of "parallel" feeders. What I see, instead, are two separate service drops, going to two separate disconnects.
If these are then combined at a panel, I see all sorts of "multiple feed" issues."
If they are segregated from each other, all the way to the outlets, then we have two separate services on one building.
As I understand parallel feeds, they have to start, and end, at the same places.....not a separate disconnects. If that is the case, I would have preferred a larger riser, with larger wires, coming from a single disconnect to a single weatherhead. Then, if the PoCo wanted to run a parallel feed, they would join at the weatherhead.