Yes, 2:28 low isn't a great time for a 30-low 10ker.
But when you take into account she ran 60%+ of the race all by herself, into a strong headwind, on a tough course, with abbreviated preparation of less than 3 months from the Olympic final plus a third place (behind just two Kenyan who are certainly superior and more experienced in the domain of marathon running). It's certainly impressive.
If Shalane could go from high 2:28 to 2:21, why not Molly to 2:20 or even better - attacking the AR.(Of course it's a bit too early to tell, though)