Take out the middle mirror, extend the other mirrors inward, and put a wider piece of trim with one scone. I would also get ride of the "transom" mirrors.

@catbuilder we already have tons of mirror because the original bathroom from 1974 was literally walled in mirrors, so I'm thinking we may as well use them. here's the inspiration pic. ( there's no window in the vanity, however. and rather than wood "transoms" there would be mirror transoms. maybe i should put 2 skinny on the sides and one big in the middle?

how about this arrangement. i put my makeup and do my hair (when i do actually do my hair) away from the sink, so it makes more sense to have a big mirror in the middle away from the sink. i like the way sconces look when they are on a side wall/mirror sticking out, but for some reason in my sketch it doesn't look right. it looks like it should be on the 5" trim directly beside the 17" mirror. what am i doing wrong. why does it look good in some bathrooms when there's a sconce on the side mirror sticking out towards the opposite wall, but it doesn't look good in my sketch? i must be doing something wrong with the trim in the corner where the side wall trim meets the big wall trim??

That side sconce is going to look weird. What is the projection of the sconce? Are you going to be seeing the reflection of the side sconce on the front left mirror? I think it will be weird to stand at that left sink , look at the mirror and see the front of a sconce and the side of a sconce ... makes it feel unbalanced.

I think you need 4 sconces all on the back wall and nothing on that side wall.

Oh, tell your contractor he is a wimp! Placing sconces on mirrors is done all the time without any issues. Well, maybe it is good that he knows he doesn't have the ability to do the work, but kind of sad that you don't get what you wanted due to his lack of skill/knowledge ...