The first figure seems thematically related to the Conquering Warrior (Front, Side) from Spiro in eastern Oklahoma. The pose is similar and, while it's hard for me to tell from the images your linked, it seems like he might also be crouching over a captive. The Conquering Warrior isn't wearing a cape, so you can see the back plate and the harness more clearly. The armor and the shield depicted here was likely for practical use, though we don't have conclusive archaeological examples of such items (ceremonial copper plates, that have occasionally be argued as decorative "breastplates" aside).

From ethnohistorical sources, we know that armor wicker and wood-slat armor and shields, occasionally covered in bison hide, were made that proved effective against arrows and Spanish crossbows (and considering that one source specifically mentions that they weren't effective against firearms at close range, they may have offered some limited protection against early firearms at longer ranges). However, while this style of armor was still commonly used in the northeast (for example, here's an early 17th Century depiction of a Wendat warrior in his armor) and along the eastern seaboard, in the southeast and on the Plains it had largely fallen out of favor by the time Europeans arrived. Shields were still in use, including large oblong / rectangular shields like the one depicted in the second figure. Unfortunately, assuming that Mississippians in the 12th Century were using similar armor and shields as their descendants in the 16th Century, this sort of functional armor would not have preserved well in the archaeological record.