Okay , I have not read the comments yet. Just jumping in to say the navy boatneck tee is FANTASTIC on you. Just gorgeous. Love love love it, and now you see why I own three of these babies and have just ordered a fourth in another colour (during the sale).
On to the spectacular amethyst sweater. What a colour on you! I knew it would look glorious on you -- as a purply pink, given purple is "your" colour. As for sizing, I see what you say about the difference in cut between this one and the V neck -- the hi-low split hem of the V neck may deal with the extra fabric a bit better....but, having said this, I LIKE this oversize look, I truly do, and I think you are not doing the sweater justice the way you are modeling it. You need to wear it as you would wear it, not with arms held stiffly, etc. Of course, I know you are just trying to show us the fit here, but you can't get the sense of drape, etc. from that. In my experience, K/R threads benefit so much from styling.
Example -- the white Zara top I tried the other day -- when I just threw it on over the skirt I was wearing, some people loved it, but quite a lot said it was a dull or not great top -- whereas when I styled it, many of those same people suddenly liked it a whole lot better.
So how about a few styled photos? Scrunch the sleeves -- I know they will not easily stay scrunched so they may need to go up to elbows.
If they stlil have it in L and you will prefer it, go for that -- by all means. The other factor we all need to recall is that your size has been changing. Your shoulders have not changed but you are slimmer overall, so a size that might have worked last year may not work as well this year.
Having said that, I purposely ordered my J. Crew sweaters oversized and so far, I don't mind it at all. Many people did not like the degree of oversize on the framed cashmere I got, but I adore it. It feels modern and fresh to my eye.