This might be bit long! I'm not the PP you quoted, but a retired marketing (and ongoing fashion) obsessive.
Any social bonding value in jeans from Tu is about money not spent. If you're interested in fashion, you'll be familiar with the mutual delight in finding the unicorn barrel-cut jeans at only £20, when they're as well-made as a £200 pair.(FWIW, Sainsbury's sold out of those within days and replaced them with a similar-looking but inferior product).
This depends on a detailed knowledge of what £200 jeans are like, and on having made bargain-hunting part of your identity.
There's a strong qualitative difference between bargain-hunting because it makes you feel clever and being forced to hunt bargains on everything, always, because you're skint. I've been in both circumstances and, while the 'choice bargain' lifestyle provided an excellent background for the 'compelled bargain' situation, the latter quickly got wearying. There's little joy in shopping the yellow stickers because you can't afford a free choice.
Sticking with food for a minute, what did I buy when I had an unexpected £20 to spend? Avocadoes and £7 bread flour instead of the £3 flour? No. I bought a single, large, T-bone steak. Every time. I could more wisely have bought a roasting joint, which would've lasted for days with the same nutritional value. But a big steak is my 'thing'. It makes me feel more human, more worthwhile, and as if I damn well deserved a chunk of prime-cut cow.
Being entirely rational, all of the time, is joyless.
So back to the branded sports clothing. Labels afford a bonding experience, we know that. Look at the handbag discussions on S&B. A professionally-built brand isn't just a name on a manufactured item, it's a whole microcosm of values. Anyone who knows the brand also knows these values, identifies with them, and identifies similarly with others who share that microcosm. It matters quite a lot, especially to young people who are still finding their tribe.
I'm totally ignorant of the specific values communicated by sportswear brands, so I'll let @WanderingStar26 get on with that part!