I've bought clothing from H&M and had zero problems with it. Same with Uniqlo, Zara, and other cheaper/cheapish clothing places.
I feel like there is a big difference between H&M and Flying Tiger. H&M actually sells useful items. Shirts, Pants, Jackets, Jeans, Suits. They all work. I haven't found them to be of poor quality.
Flying Tiger on the other hand seems to sell mostly useless stuff meant to give away at a white elephant gift exchange and then thrown in the trash.
As some economists will argue, being able to by clothing for less allows poorer people to buy clothing and allows all people to spend more money somewhere else (food, shelter, education, entertainment, ...) so it's hard for me to see how H&M is hurting things but maybe I don't have all the facts. I know they do have a recycling program. I suppose you could argue that's part of the problem though.
It does works but the quality control is questionable. You will often find poorly done and finished sewing or pieces which are cut approximately. They also often use the cheapest fabric they can get away with. It leads to clothes which really don't age well.
Where I agree with you is that a lot of brands which present themselves as mid range actually don't do much better and are just selling over-priced pieces.
Also national stereotypes are weird.
Considering the amount of glues and plastic required to make IKEA furniture I'm not convinced even at the 10 year mark IKEA is better ecologically, but that is a complex question that I wouldn't know how to analyse (if anyone tries I expect a few years latter someone will find a significant factor they didn't account for, and again a few years latter...)
Even if you're right, moving frequently is a fact of life for young people who grew up away from the west/east costs. It's the only way for young people who grew up in the midwest to launch a successful career.
Hometown --> college --> internships --> back to college --> grad school --> first job --> second job --> etc.