Well, that’s a matter of opinion. Strapless styles may be universally flattering on young, slender women, but I have seen some “fluffy” girls stuffed into them where the result was, shall we say, less than to be desired. I’m with you on the cleavage thing, though.
Personally, I refused to wear any sort of dress that required me to wear a strapless bra. This was more about comfort than modesty, since I am a bit on the “fluffy” side myself. Maybe strapless bras are better now than they were back in my day, but in the ‘70’s, they were extremely uncomfortable for anyone bigger than an A or B cup. Lace-covered torture devices they were! I’m just glad that as a musician, I played my flute for all of my friends’ weddings instead of being a bridesmaid! The only bridesmaid’s dress I ever bought was for my brother’s wedding.