"Men, in general, don't care about symmetry or aesthetics for the most part. :(" Umm, No. Just No. So, first issue is "centered on what?" Is that the entire wall where the faucets are - or is that the space defined by the interior of the shower. I can't really tell from the photos, but it almost looks centered on the interior space of the shower. Yes, the centerline of the drain and the faucet/shower head need to be on the same line. There should be a drawing, and it should be initialed. It should show the location of the faucets, shower head, etc. and where the centerline is. If you have questions, you need to get answers before the tile goes up. If he mumbled and you didn't understand, then the two of you didn't communicate. My guess is that the new centerline is blocked by that stud. Fixing it would require cutting the stud and re-framing that. It would also require some mud / paint in the hallway. Doable, but the scope of the project just got larger. The new centerline may also be blocked by a floor joist (the drain). If that's the case, it may get much more complicated. All of that should have been decided once the old tub was out and you could see what you were working with. I'm not saying the contractor was not at fault - he should know how these things go. But I also get the sense that clear communication wasn't happening - and that's on both of you. Drawings need to happen - or be updated - once you have done your demo.

If the 36" tub fits and allows the proper on-center distances for the toilet, I don't think the wider tub will have any negative effect on the size of the bathroom, because it is at the "end" of the bathroom, and it may be a more comfortable tub for someone to use, compared with the narrower one. If you do not have a walk in shower, I would probably replace one of the tubs with a walk in shower of the same size as the tub. It's easy enough, doesn't change the plan, and may be useful if someone breaks an arm or a leg, or has trouble climbing over the rim of a tub. Or standing in a tub to take a shower: sometimes the bottom of a tub is not flat enough or wide enough for someone who has balance issues.

I like the suggestion that Annie gave about using four chairs facing one another. This is a really cozy arrangement especially if you want to relax and converse with friends. It's not that I don't like your mantle, but it's not that French glam that you're seeking, so I'd replace it with a beautifully carved one. I'd spray paint the bar/tea cart gold and use some Rub & Buff to give it a nice vintage finish and then place between the two chairs. If you use this configuration make sure to use a 8' or 9" square rug. They're harder to fine, but they're out there.

What size is your sink? Is there a chance of doing a smaller sink base ( 3") and shifting it to whichever direction it needs to go and adding a 3" filler to the opposite side? This would make the sink only 2-3" off center. Do you have the actual floor plan noting all the cabinets you are getting? I never think a faucet off center is too bad but the sink and faucet are off cent on a 3 window set up - that will be much more obvious. I understand the design plan had to change, but this feels not quite right. I think I would order a slightly smaller window that I can center on the sink and then replace one wall cabinet and make it bigger. And forget about centering in the room . Have your designer put that in the computer so you can see it that way.