I've had a 5Ds for almost 2 years not. Picked when up when Canon was doing the firesale clearance and bought a refurb from Canon. It's a lovely camera, and is currently my only DSLR. I also had a 5DIV paired with it, but then got a R6II and one of the DSLRs had to go to help fund the purchase. I chose to keep the 5Ds. The 5DIV was absolutely the better camera in every way except resolution, but since the R6II is now my "do everything" body, I kept the 5Ds just for that amazing sensor. It's still a pleasure to shoot with.
As I'm sure you're aware, the limited dynamic range was the main weakness all the reviews pointed to when the camera came out 8 years ago. And yes, it is a noisy sensor that will get ugly in a hurry with extreme editing. I've found that DxO RAW processing software does an amazing job with noise reduction and cleaning up the shadows on this camera. I was an Adobe RAW user for years, but for this particular camera the difference was shocking. Using DxO on this camera felt like a sensor upgrade. The camera is still a noisy beast, but whatever secret sauce DxO uses, it works fantastic.