I was a little surprised to see SPCR choosing the windowed version instead of the nicely damped solid side panel though. I wonder if that was part of the problem with the hard drive vibration issue? That window looks like a great design for a case vibration amplifier, especially since you mentioned it was mounted a bit loosely.
I would totally prefer the non-window version, but that's what Fractal sent us. That being said, I pressed down on the window and various other points around the case during testing to see if there was anything structural that could be done but it was constant.
I would loved to have seen a direct A-B comparison of this case vs the R5 Gaming build to find out if/how much the changes benefitted thermal/noise performance. I still rip CDs, and my Windows install is still on a disc, so there's the occasional need for an ODD. If there's not a big thermal benefit to the ODD removal, I'd rather store the ODD inside the case than need an external drive to occasionally plug in.
I can't imagine there is much a difference at all as the cases are so similar. The test results for the Define S should be identical to an R5 with its main drive cage removed.