Without the steel reinforced concrete support the wall would collapse .

Quartz is not exclusively associated with Neolithic monuments , it is found throughout the EBA to LBA too and possibly more common in the BA .
The more recent Lynch and Sweetman excavations show that there was post Neolithic activity in the area of monument, exactly as is found at other major monuments including reworking of older material e.g. Stonehenge etc and also noted locally by Eogan at Knowth . Later BA use of the sites , and or reworking , of earlier monuments is the norm .

Yes the pic shows that the quartz that makes up the wall is nothing like the walling found in other monuments . Quartz is far from ideal because it doesn’t fracture along structural planes and produces far from rectangular slabs that are useless for walling .
"A good quantity" of the original quartz that was discovered " was shattered and could not be used " on the facade , coupled with the much greater extent of the facade compared with what O 'Kelly describes , much of what we see must have been imported for the job .