They should be a big step up from V's...a lot of people are running the trail version on DH bikes.
Isnt that m980?
985 for the race and 988 for the trail...minimal differences between them. Race uses a smaller diameter lever and no tool free adjust. These are super powerful, I think the previous generations, which I've just twiged that the brakes in question are can be a bit squiffy, like the XT's your mate is ditching. I think they can be a pain to bleed and set up compared to previous Shimano brakes, which is where the issue may be coming from.
Even if the previous generation brakes aren't as powerful as the new ones, they should still be better than rim brakes. Even C2's managed that and they're pants compared to modern discs.
2015 Stanton Ti Switchback
2006 Specialized Demo 8
2013 Specialized Allez Sport
1999 Santa Cruz Chameleon
1994 Cannnondale Beast of the East (rebuild still in progress)