In the most literal sense, if we are only talking about the *course* itself, and not the weather, it is actually a pretty good course for a PB. Net downhill, and the hills aren't terrible. That said, I do think a pancake flat course is slightly faster (unless you're a really good downhill runner).
Now, if we add in the weather (which I'm sure the author was thinking about as well), then it's a complete crapshoot. I would not register for Boston if my sole goal were to run my fastest marathon possible. In my mind, weather is more important than course profile, unless the course is mountainous. As we all know, Boston can be obscenely fast (2011), ridiculously slow (2018), or anywhere in between. If you had a Breaking2 style schedule, and could pick the day you ran it, then Boston would be consistently fast.