They’re semi-randomly generated in that each floor has certain stuff that will always appear from a short selection and a certain number of things like shops.
Removing cards is very strong but it’s not essential. Especially in Ironclad with all the ways it has to exhaust cards. Plus there are ? encounters that remove or upgrade cards and one that even upgrades every strike and defend card in your deck, so they’re no longer rubbish.
The hardest bit of StS is evaluating cards and I’ve changed my mind on so many of them after seeing what they can do, or after being underwhelmed by them. Comes with more runs.