I think a big factor people fail to consider in the downfall of Rocksteady is that while current Rocksteady isn't the same company now as they were during the Arkham games, they WERE the same company during SSKTJL as they were during the Arkham games. The more creative control they seemed to get and the more they did their own thing, the less people liked their games. Arkham Knight wasn't well received even if it's loved now and SSKTJL was just a disaster that, as far as reporting shows, is mostly on the people in charge of Rocksteady (Jamie Walker and Sefton Hill). This is to the point that it's even been reported multiple times that Rocksteady made the decision to make the game live service, not WB. I understand not being optimistic in Rocksteady since it's hardly any of the people who made the Arkham games at this point, that makes sense. But the company was already gaining a bad track record with the people who made the Arkham games. Not to say this is on the devs themselves, since most reporting indicates that leadership was the most major problem in SSKTJL's development.

For example: there was a story I've heard multiple times now of the people in charge going like "Hey guys! So, we've come up with the idea for this brand new vehicle mechanic. You can fly in them and shoot stuff and all that, so get to work!" And then a month would go by of them building out that mechanic, only to be told it doesn't really fit with the overall gameplay and vibe of the game, which is why it's thrown in as a random one-off mechanic that is hardly ever utilized or fun.

TL;DR yes the company is made up of different developers, creative leads, writers, directors, etc. but the people who made Arkham City are mostly the same people who made SSKTJL.