Mech discs have an issue with housing compression. The small rotor and compared to a 29er rim size means a disc pad has to squeeze much harder vs a rim brake on the same wheel. The increased force ends up compressing the housing rather than ending up in the pad. So you may want to think about upgrading the cable housing to something designed for higher forces like Nokon.
Cable discs have no more problem with housing compression than rim brakes do. This belief is a result of incomplete understanding.
There are two types of cabled discs, road lever compatible ones and long travel lever ones. Road lever discs, by virtue of using the same lever, will have the same cable tension as a road rim brake if the lever effort to stop is the same and anyone who uses discs brakes can tell you that discs do not require more lever effort. Mountain variants, because of their longer cable travel, will need even less tension.
How much lever effort is required depends on brake, pad material and choice of rotor, of course, so there is a setup component. That's true of rim brakes as well. It's conceivable that a disc brake could be set up worse than a rim brake but that's meaningless.
So what of vik's "small rotor" explanation? It's true that the effective rotor is smaller but vik is assuming the coefficient of friction is the same which is unlikely. That's not the killer, though. Squeezing the disc pad harder does not mean more cable compression because the leverage inside the caliper itself is radically different. Rim pads must travel a great deal further than disc pads so a disc brake has a huge mechanical advantage inside the caliper. Remember, if you are using the same lever and squeezing less on it to stop then you are using less cable tension regardless of what "experts" say in the blogs and magazines that earn them money.
If your lever effort is too high, get a bigger rotor, not the most expensive cables you can find.