Another rubbish thing is that Vora's wand didn't have a buffer. It's actually retarded and not much more than for plot value. I have strong doubts that any sa'angreal would pass quality control without a buffer.
I agree that the fact the lack of buffer was not mentioned is a huge gaping plot hole. Egwene used it like a hundred times on screen, and she never thought about the risks? No one warned her?
But I don't think its implausible that there were extremely powerful sa'angreal made towards the end of the War that weren't perfect. We know the CK didn't have buffers, and it may be that other strong sa'angreal like Callandor and Vora's Wand also had this problem in the end.
No, Callandor has no Saidin buffer. That's why you need to be in a link with 2 women to use it safely.
The shield thing makes no sense, agreed.
But the matching thing can work. So far as I know, sa'angreal let you draw a set amount, no matter your potential. It is conceivable Vora's Wand was made to match D'jet.