CG is way better than a LOT of restaurants in NYC...and not as good (i wont say 'worse') as many others. but you sure as heck wont find people dressed the way some find acceptable at WDW signatures as MOST NYC restaurants, regardless of price point or acclaim unless you're at a tourist trap in times square.
But this is entirely the point. People who live in NYC have a fashion sense unto themselves that you wouldn't even find in other major cities like LA or Chicago. Seriously trendy fashion and clothing that would be incredibly uncomfortable in a theme park. I lived in NYC for a decade and now live just outside of it in coastal CT. Literally 50 minutes away, but people in NYC wouldn't be caught dead in what is fashionable here (think Vineyard Vines). You aren't going to find New Yorkers at a Times Square tourist trap. You are going to find tourists who don't dress like New Yorkers at the tourist traps. Most people who go to WDW aren't from NYC, so I'm not sure why we are expecting people at WDW signatures to dress as if they are going out in NYC?
When you travel to WDW, there are so many factors that come into play in terms of wardrobe including luggage restrictions. People typically have to pack efficiently to accommodate the environment they are traveling to. In WDW, that includes, mainly, park touring which means comfortable clothing and footwear. There is no freaking way I'm packing a pair of 4 inch Jimmy Choo's and a separate dress and handbag simply to please my fellow CG diners.
This debate has been going on for years on these boards. I personally don't care what other people wear and it doesn't affect my dining experience. What others wear is completely out of your control, so why let it negatively impact your experience?