Example: Vambrace and elbow cop. If the "shell" material doesn't deform, when you twist your wrist the vambrace will either align with the elbow, align with the wrist, or align along some line in between. What it isn't going to do, under any provocation, is deform itself along a spiral so the wrist end of the vambrace aligns with the wrist and the elbow end of the vambrace aligns with the elbow. Ain't gonna happen. The elbow cop always and forever moves with the elbow, so to whatever extent the vambrace "follows" the wrist, it's going to misalign with the elbow cop. When the edges of shell material meet, it's not going to move any farther without deforming the shell material. To whatever extent you cut back the edge to gain freedom of movement at that extent of the twist, to exactly that same degree you leave a gap in the shell material when motion is at the opposite extreme of that same arc of twist. You can flare the edge out rather than trim it back to cover that gap, but flares... flares are good at shedding force on the outside of the flare, but on the inside of the flare they channel it inward. Poorly designed flares can get you dismembered, turning "slash muscles and tendons" into "sever joint."
Note that all this assumes no magic. Give me unbreakable elastic magic bonds between plates instead of leather straps, and plates that continuously remodel their own shape off of the shape of the body part they're covering, and I'll give you a set of full plate that you can do Olympic gymnastics routines in.
A "Dwarf master armorer" may just be some guy who has been doing this so long that he has learned how to:
Make very flexible steel. Useless for blades and armor, but makes good wire.
Draw extremeley fine wire.
And thus,
Make steel mesh and stranded steel cable.