It is possible to have an "original" blast white coin and to assume that a coin is "unoriginal" simply because it is blast white is simply not a fair assumption. Yes, toning can look pretty BUT the reaction which "causes" the toning is not always a good thing.
Sure it is...maybe not with newer coins, but as silver ages it tones. Simple as that, it's a natural chemical reaction that happens due to the air. Storage can slow it down, but as along as there is air present a silver coin will tone. It might have minimal toning...but all those completely blast white Morgans you see...they have all been dipped. I agree...it can be damaging to coins, especially if the toning gets too advanced.
If I remember right, this was listed on Great Collections last week, right? It caught my eye, but the price was a little steep for me. I personally would love to own the coin. I think it could go either 65 or 66. Just depends on the mood of the graders that day...
I think it is entirely possible that the eye appeal and luster of this coin pushed it from an MS65 to an MS66. I don't think there are nearly enough distractions on the surfaces to warrant an MS64 grade based on the MS64s I have seen in the past. Sometimes it is helpful to view a zoomed out slab photo which will make the hits on the coin appear the appropriate size. As for the size discussion, the TPGs grading standards are based upon market grading. So when we are asked about the grade of a coin, it makes little sense to use technical grading in order to criticize the assigned grade.