The problem here is that the question is one of balance. And the last time the base fighter class gets something genuinely new rather than a single extra use of something they already have or an option that wasn't good enough to choose last time is level 11 when they take the lead for attacks per round. And level 11 is basically the last time the rogue gets anything new that they can actively choose to use rather than reactively. Most people don't of course go much above level 10
Them picking what they like when there is an imbalance isn't them "Getting it". It's them picking what they like.
The imbalance still exists. Being able to ignore a problem doesn't mean there isn't a problem. See literally every ill that has existed since recorded history. From Warfare to Price Gouging to Favoritism to Lying. There's always going to be people who can ignore it, that doesn't make it good or just or right.
Speaking as someone whose group regularly plays well into the teens (all the way up to 19th level), I don't entirely agree with this.
In terms of depth, fighters and rogues can hold their own against casters all day. A high level martial character is a demon on the battlefield (and the rogue's skills can do plenty off the battlefield as well).
I think their issue, such as it is, is breadth. Casters, as they level, gain breadth and depth. They get stronger spells, and they get more of them. Martials, primarily gain depth. They don't really get much more that they can do, they just get better at doing what they already do well.
While this is imbalanced in one sense, it isn't really imbalanced. There was another edition of D&D where, when I experienced it, the martials were an afterthought. If they hadn't shown up that night, I doubt the casters would have noticed. And you could tell that the martial character players weren't exactly enthralled by the disparity. 5e isn't like that IME. Martial characters are very good at high levels, and if they're missing for a session you will most definitely note their absence.
Don't get me wrong. I would very much love to see high level martials as mythic, based on archetypes such as Beowulf. That would go a long way towards giving them the breadth they lack. However, as it stands I don't think they are unbalanced per se. Just more limited than their caster counterparts.