Flex in the system is the villain.
It sucks up cable pull and it is only once all the flexy components are fully flexed that there’s cable pull for your actual braking.
I suspect how good (or bad) cantis are has a lot to do with how much your frame or fork flexes when the cantis are applied.
If you look at the light stays and fork legs on a CX type bike it’s no wonder it’s hard to make them work. A lot of the cable pull is used up just flexing them apart which is probably why a brake with more cable pull like a V-brake works better.
I remember wondering if it would be worth using reinforcement (booster?) like the Magura hydraulics used, but then realised it was simpler to just use the Maguras. 🙂
Really good brake outers make difference, as they do with any cable brake.
Many dropbar road levers also had more flex than I like, and that also sucks up cable pull too. (However I haven’t experience of any of the latest ones so whether that still applies, I do not know)
And then there’s the black art of getting the straddle cable just right. 🙂