Lots of treatments are legal it is a matter of when they are given and if recommended dose rates are exceeded, this is where the problem lies. If cobalt does not give a horse a "boost" I am pretty sure people wouldn't be giving horses excess amounts. Hard to say some people are not using more cobalt than other people when many horses levels are <5 compared to others over 20 or 30 and some over 100.
I'm with you Stu.