I hope you're not capping your sit down restaurant tips in America. Most more expensive places have waiters working far fewer tables so they can be more attentive, and they're also usually the cream of the crop waiter wise. The higher total tips but still a normal percentage are definitely what they need/deserve to make the longer meals and fewer tables make sense financially (assuming the service actually was good of course).
Note I'm not advocating for any of this "20% is the new baseline" bullshit, but you definitely shouldn't be capping your tips. Same goes for capping your bar tips unless you're talking about only pouring wine/drafts or opening beers, and then I'd still advocate a per drink cap of like a buck per - definitely not a total cap.
It's a question of opportunity cost. In order to be really attentive they work fewer tables, so they need to have higher margins to make up for lack of volume. If you can't afford a 15% tip, or 20% for good service, you shouldn't be eating at an expensive restaurant to begin with. That's the social compact in America, that's how it works. Until servers start being paid a living wage, you're not the arbiter of what constitutes paying "enough", you're just rejecting cultural norms and hurting servers so you can save a few bucks.