Many coaches preach landing on the ball of the foot. Reasons include (1) being on the heal is not a position of good balance and (2) there's often a hole where your stride foot plants and landing on your heal can increase the chances of your stride foot slipping.
I feel it is next to impossible to land on the ball of your foot if you are taking a nice long stride and I use to teach landing flat-footed. But now I no longer worry about it at all. If you're getting your hips going and building up momentum to get into foot strike quickly, then even if you land on your heal it will only be a millisecond or two before the ball of your foot hits the ground and your weight is shifted onto it.
I say landing on the heal is normally a non-issue. If, for some reason, it is an issue, I think the fix is in building up more momentum - not worrying about what the foot is doing.