Worlds alternates, being named later, ended up having Ava Ziegler as 1st alternate ahead of Elyce and Starr, which very few could quibble with (maybe only Sarah Everhardt being totally passed over being an issue, although she would've needed min scores). Going into Nationals, most probably felt that Isabeau and Amber were something of a near lock for Worlds. Of course Ava and her team were the ultimate decision makers for the decision to withdraw from Nationals, but I think there is a lot of credit due to her for both her very strong season and ultimately making a very smart decision, which ultimately could have put her at Worlds if anyone withdrew. I still think the rules should be amended to clearly state this type of a bye, but ultimately this does make sense. In winning NHK, she defeated a World medalist and a European champion. What is unknown is if she actually has been skating/jumping and reasonably could be expected to compete at Nationals.
All that being said, I feel Alexa Gasparotto and Brooke Gewalt deserve to be at Nationals also. Both can be true. I think there should be a caveat on senior level that if your score beats out 3/4 of the other sectional qualifiers, you get a spot. Of course that would eliminate their neat 18 person limit, and would never happen, but I think it is warranted and only fair given how strong Mids was this year.