Why do you say that? I've had Magura rim brakes on our tandem for 12 years and only ever had to change the brake blocks and their stopping power is great and if you've ever descended long hills on a fully loaded tandem as we have many a time, you do need good brakes and the Maguras fit the bill.
Maybe you poor experience was down to something other than the brake per se?
Our solo (early Motus hub gear) has HS11s. They brake reasonably well when bled/adjusted but are a pain to do any work on; much more difficult to adjust than the V-brakes on our tandem and only marginally better stopping power.
Other owners of HS11s might comment. The main difficulty in adjusting is that even with the brake tightening screws properly loosened the brake holder and pads do not slide easily forward and backwards. They need quite a bit of pushing and even then move very jerkily making it difficult to set to any precise position.
I wondered if the previous owners might have done something to make it misbehave?
Does anyone else have similar issues?