One way to deal with this is to use the 'Report This Item To Etsy' tool, found on the right side of the page (about the bottom of your screen). One of the options is 'incorrect tag or category'. There is space to add details or explanation, but it's not necessary.
You can't reasonably expect Etsy to monitor every single listing - they'd have to pay someone to do that. But reporting an item helps straighten these issues up. I've noticed a number of these listings are relatively new sellers, so they're likely clueless and would benefit from receiving a nudge from Etsy.
Items made from vintage materials and altered vintage items do not belong in the 'vintage' category, however, they can use 'vintage' as a tag.
I noticed this last week but have also noticed some blatant vintage mistagging - Tagging a necklace as a brooch, necklace, bracelet, earrings etc...and no it's not a set or demi. We must still tag with vintage first and I think that I'll be doing a little letter writing on this as it does give many an unfair advantage. I would also think that those who are handmade must be furious and I'm sure they are taking some kind of action. I wouldn't be surprised to see it resolved shortly.
Great topic - it was on my mind and I just haven't had a chance to act on it...thank you for bringing it back to my attention:)