Thats kind of my reasoning for them NOT doing the striking as heavily and why grapplers were able to dominate the challenge matches. Strikers have to pull back their power, speed and contact to not damage their partners. Meaning that they are going less than full speed and power when training with a partner most of the time. Grapplers can go all out, full speed and power when applying thier techniques. As can their partners when resisting, the feeling of making something work against live, full force resistance lets them get a lot more quality training in a shorter time.
You can get around this in striking by using pad drills, but you have to double the amount of training time to teach students how to hold and feed to mimic real life encounters and get some sense of realism in the pad drills. This usually takes a few months to get down. You can get a grappling move down in an hour if you rep the hell out of it.
Everybody knows how much it sucks to get a holder that doesn't know what they are doing, you might as well be shadow sparring. With grappling, all you need for a partner to know is that they are supposed to grab, push, pull and squeeze as hard as they can to stop you from doing what you are trying to do.