3DMark isn't useful for determining whether a card is fast enough to play any particular game. But that's ok because that's not its purpose. It's job is to be a benchmark of "relative" performance.
Back in the day 3dmark would also provide a glimpse of what's possible with the latest rendering APIs and algorithms and that was a very useful and exciting thing to have. Now the last few versions have just been an ugly, unimpressive mess with no value whatsoever. 3dmark Vantage was a joke and the others haven't done much better since.
Considering it as a benchmark of relative performance is dubious at best. I can tell you that system A gets 11 units of performance and system B gets 18. What the fuck does that mean? It doesn't translate to anything. Sure you can look at the system specifications but it doesn't tell you how to get more units of performance or what system components determine that level of performance. X units of performance do not necessarily translate into faster Handbrake encode times or better performance in the Doom Beta.
3D Mark is arbitrary nonsense.