Those other well known methods also support efficient addition and removal. Supporting weighted devices is a tweak that should be obvious to any competent engin

Those other well known methods also support efficient addition and removal. Supporting weighted devices is a tweak that should be obvious to any competent engineer, which I know because I've done it myself in a similar system. The paper might reasonably claim their way is better, but to represent it as a qualitative change granting never-before-seen capabilities is to misrepresent the state of the art at the time. The only comparison where that works is to Lustre's "MDS controls all" approach, which most people working in the field at the time (but apparently not the buffoons working on HDFS) already knew was bad.