i don't think that's true at all. in the case of Ashley Wagner, she continually showed up in international competition, worlds included, the years before Sochi selection. she won major international medals competing against the sports biggest names. she won and kept Olympic spots at worlds. she had a bad competition at nationals that season, and it was her body of work that got her on the team, deservedly so. she had already proved she could show up when it counted most, under the highest pressure, and win medals for the US. the federation could trust her on the biggest stage.
On the opposite hand, this is exactly why Ross Miner was not selected in 2018. he had one amazing competition at nationals with nothing else to back that up. he hadn't won an international medal in over 2 years and hadn't even been on the national podium in 5 years. he couldn't deliver when it counted. USFS couldn't count on him. this was also why Amber was not selected for worlds last season. they aren't going to pick a skater who showed up one time to represent them on the biggest stage in the sport when they already couldn't show up on smaller stages. it is a huge gamble and risk to select a skater who is inconsistent and can't hold their own in international competition. IMO the risk well outweighs any possible reward and it's not worth throwing the dice.
Definitely not trying to rehash any of that, just providing those situations as examples why i don't think it makes any sense to put so much weight on one competition in the whole entire season, and a domestic one at that. nationals should absolutely count and hold a lot of weight, but it should not be "trials" or the deciding competition when many times it hasn't been a representation either way of what a skater can or cannot do.