Brands like Alpkit have done exactly that, using reasonably good down for a good price. They manage to do this by reducing the chain.
There are a whole lot of costs in the whole process. If an item retails at 120, vat will be 20, trade price around 60 leaving around 40 for the shop. Any discount they give is taken out of this profit (ie they don’t get any further discount from the supplier). In other words, if they offer 20% discount (24 pounds) their profit is then only 16 pounds. (Well, not quite as Vat will also change, but you get the drift)
If made in China, clothing will have import costs and duties ( totalling perhaps 20%) so product is now down to about 40.
Down is pretty expensive, and making jackets is a relatively complex pattern (lots of baffles to hold down in place), plus the company making the jacket needs to pay workers and make some money.
I know kit seems expensive sometimes, but there’s very few people in the industry getting rich. There are a few exceptions of course!