They skated clean and got the most points with the less difficult elements. Teams that most often skate clean with more difficult elements made big mistakes. C/L backed into the win.
I would agree with you regarding C/L's national championship. C/L did complete their elements and did them well. Simply their elements were not as strong as the other key teams especially when it comes to the lifts, and in a way they backed into winning. Put is this way if everyone delivered there best performance who would win? It's about chasing points and I would rather have the big tricks like Alexa and Chris did with the twist than relying on someone else to make a mistake.
If everyone delivered their best performance, we don't know who would win. We can look at the scores and the past performances during the season, but we still wouldn't know who would win. Anything can happen in figure skating; that's why we watch it. Having said that, if Tarah and Danny had completed their aborted lift at Nats and scored high on it (a Group 3 level 4), they might still have finished anywhere from 3 to 6 points below Ashley and Tim. For one example, at the IdF 2018, that lift earned T&D 6.63 points. K/K had a difficult year, and that's part of the sport too.
I disagree with your opinion that Ashley and Tim "backed into the win." Ashley and Tim delivered at that competition, and also at 2019 4CC and Worlds. They had to have big tricks to win any color championship medal, as
Spiralgraph said. They also performed all their other elements at a high level, gaining excitement and momentum as the FS progressed. That's what happened with Alexa and Chris's SP at 2020 Nats, and with Jessica and Brian's FS. That's the way it works.
A&T had a difficult 2019-20 season. Just like every other US Pairs champion has had in their subsequent season, since 2014, including Alexa and Chris, twice.
Having said all this .... there are many other factors than big tricks that make a great pair. For me, Ashley and Tim elevate all their elements with their passionate performances and their musicality. Emotion invites audiences in. The power of their performance is elevated when you're in the arena. I love their synchronicity, their conviction, their presence, their matching lines, and their dedication to improving year by year. These are all, by the way, things that elevate Sui and Han above the rest. Yes, S/H have high quality, consistent technique. And if you look at their skates since 2012, they improved vastly over the years, one step at a time. Most of the teams A&T are compared to have been partnered together since 2012, as opposed to A&T together since 2016.
Ashley and Tim are one of my many favorite teams because of the experience I have when I watch them skate, either in the arena or by video. Beauty, passion, attention to music, connection are more important to me than who wins. Sure, I like it when they win, but ultimately I want to see them continue skating at the World's Top Ten level, because I greatly enjoy their skating and their partnership.
Daddy Ash is a taskmaster! 
Really striking.
I wasn't watching skating during that time, although I did somehow see him kneel and propose to her on the ice.
??
