RawTherapee is great in most ways, except that all of the curves for adjusting anything have absolutely catastrophically bad handling. It's so amazing having access to the Lab colour adjustments but the sliders are abysmal, impossible to make any kind of precise adjustments, impossible to reset an individual slider/point back to it's default placement, impossible to undo the last action without resetting the entire widget to its default state. It's unusable, and I'm convinced that the popularity of it would skyrocket if they'd finally just sit down and address that it's miserable to use. I would drop lightroom in a heartbeat if they made them even a little bit better.

I know it's a different space, but as a counterexample, FabFilter makes audio plugins that are the gold standard for that kind of interface and it isn't even close. Anybody making an interface for interacting with points on a curve should sit down with the free demo of FabFilters Pro-Q3 for just a few minutes to experience what's actually possible and how it should feel.