You are garbling the tiers.
2017 Nationals are in Tier 3, not Tier 2. (In Tier 3, along with 2017 Challengers.)
2017 Four Continents and 2017 GPs are in Tier 2.
Worth mentioning b/c for example:
Would Mirai's bronze at 2017 Four Continents be worth as much as Ashley's bronze at 2017 Skate Canada?
IMO, seems very possible.
Likewise, seems very possible that Mirai's 2017 Challenger silver (at U.S. Classic) would be worth as much as Ashley's silver at 2017 Nats.
At this point, it is possible that Ashley's 7th place at Worlds is her "only" real bump over Mirai.
Remains to be seen whether the bump will come into play and how valuable (or not) a bump it would be

.