The Magura brakes don't take 50 or more feet to wipe the water off the rims. Some moron in heavy traffic and in the rain, brake checked me several times and I didn't hit him with my tandem.
In the famous tandem group coast-down on Mt. Ventoux, the rim brake bikes were the only ones not to have issues. There were no Arais (2 lb. penalty). Overconfidence and maybe lack of feedback. I know several rear disk bikes which have warped their disks, one that overheated - the bike went into the woods but was OK. Nothing's perfect except maybe dual disks with big laminated rotors. But there's the weight again, so kinda back to the Arai. Gotta get ride of the heat somehow. But disks are certainly potentially safer. Arais don't do what they do.
That explanation was quite convoluted. A drum brake used to keep speed in check and rim brakes works the best. Disk brakes on a tandem are not adequate. Some of those riders had melted pad adjusters and warped disks and no brakes. There is more heat than they figured in the disk design. Or they just didn't care what the average riders skill level was. The Arais was not a weight penalty. It has more to do with available equipment at the time and in the case were the weight weenies shaved the cooling fins off and crashed IQ quotient.