That's a legitimate concern.
If the demand for those rides falls to the level of Everest and Safari, what would be the point? Do one and secure a fourth fastpass for the other. It's not going to get many to spend two days unless they were already going to if the demand isn't there anymore.
That said, AK is a multi-day park for my crew so it's not a huge deal to me, but tiering in general is annoying. It certainly highlights the need for more demanding attractions at Epcot and HS. Here I could see the argument being that they need to spread out the newness. Hopefully, that's relatively temporary.