From my experience, dressing up certainly isn't required. We recently flew F to Oz and back. On the way out both my partner and I made an effort to dress up. However, after a couple of weeks in the sun we really couldn't be bothered and I ended up wearing shorts for the segment from SYD to BKK and a pair of scruffy jeans and trainers from BKK to SYD.

From what I could tell it made no difference either way to the service level that I got. On all sectors the crew were fantastic.

Methinks maybe the OP got a bad crew or else was a little too sensitive and read too much into minor oversights that were not intended to belittle?