Yes, except the last bit. I know personally of a guy who set up a coffee hardware company - I think he got to £3M turnover in 5 years, at something like 50% markup. Some yank sued him for infringement of copyrighted aligator emblem, took half a a mil out of court. The guy sold the business, now lives in Portugal. He used to work for the BBC....Most Chinese sellers on the selling platforms are just resellers, selling the same stuff from the same warehouses.
There are UK and EU customs warehouses who specialise in this. A supplier sends the stock to the warehouse, who store it in a bonded warehouse. Reseller does the legwork of selling it, who once sold send payment to the supplier, then the warehouse gets paid to sort out the official import and arrange delivery to the buyer.
It's why you'll often find the same product will go out of stock at various sellers at the same time.
Big exception are those doing the full Amazon FBA thing, where there is no middle man. The (re)seller has to have their own stock in Amazon warehouses, and the import tax to already be paid before it gets there.
Then there are those shipping directly from China, but again, it's largely resellers selling the same stock from the same warehouses/suppliers.
It's all a numbers game.
Nobody at any stage is really making that much margin, they're just selling enough to make a reasonable living.
Some might get lucky with a particular product and make a relatively huge margin, but it doesn't last long as there will soon be somebody else undercutting them.
Edit to add pic of the coffee pot his dad gave me - apparently if the packaging is slightly damaged the German customers complain, so his dad had a shed full of new stuff...