What do you have against tincans on horses ?
Let it be, it's a necessary money sink.
Or did the well-known 1h-steel shield armored cav tincans twins roaming eu1 killed you too many times ? They're tough fellow indeed, but for the sake of economy, i'll let them be.
Though on a realism point of view, if the horse is already carrying 100kg, i don't see how carrying an extra 10kg can change much. Also, if you're counting armor, you should also count the weapons weight, and shields.