How practical would shieldbearers or the thronebearers be in real life?

I was thinking about getting the new lord kit and inmediately thought about how uncomfortable it must be to use one of those for combat: You are pinned down to the shield surface to fight and you would cosntantly rely on the bearers not getting tired/killed to stay up there. Why would a dwarf lord/thane expose themselves in that way? I understand that it gives them some high ground (*Obi Wan nods in approval), but I find it way too unstable to be used in real life.

What are your thoughts?