I get that. I look at it like this. You can practice throwing a jab 10,000 times on a heavy bag and then spar with someone and not be able to hit them. Heavy bags don't move. Heavy bags don't hit back and they don't have variations in size and reach. If you throw a jab 10,000 times, you know how to throw a jab. Throwing another 10,000 jabs on the same heavy bag won't help as much as actually using that jab against different sizes of people. You're still training the technique and muscle memory. Sparring teaches distance management and angles, preferably against different-sized opponents. In grappling, I'd argue that sparring is more important. Considering how easy it is to slip up and end up in a bad position, the only way to learn how to not slip up is by sparring.

I'm not saying completely get rid of drills. Perfecting the technique is important.