New iMac 5K 3TB force closing apps, won't wipe hard drive

Question

This is my first Apple computer purchase. I've been in PC support for many years, and this has stumped myself, two Genius reps, and a Cupertino engineer who just so happened to be at the store I took it into. Keep in mind, I received this computer FIVE days ago.
I unboxed it, set up a user profile and installed some Adobe products and a App Store app called "Timing" to track how much time I spent in each project. Three days later, I had some issues where the RAM (it has 32GB) was being used up completely by Adobe After Effects and Premiere. I was working on a 1920x1080 video for web. Both programs kept freezing and force closing every ten minutes, saying I was using up all of my RAM. I checked the Activity Monitor, sure enough - 11GB of RAM was being used just while idling. AE and Premiere would take it over the top. I deleted the "Timing" app and it seemed to stop doing that. But the thought of running into this problem neck deep in a render terrified me. So I decided to do a clean OS install, just to be safe.
I backed up my work, disconnected my backup drive, booted to the disk utility. When I got into the utility, I attempted to delete the Hard Drive but got the spinning pinwheel of death halfway through. A few hours later I hard rebooted and tried again - same thing. I thought, maybe it erased the hard drive but was just hung up. I advanced to the OS install and left it to download.... something that had to do with the OS. The next morning, I shook the mouse and my user profile login appeared. Exactly nothing had changed, or been deleted. I called Apple support and a very nice lady walked me through a fix (the exact same thing I had already tried, of course). We went through the fix, but this time deleting my iCloud and gmail accounts within the OS and THEN trying to wipe OS, in case it had restored my computer via iCloud after the wipe. Same exact result, error while erasing the HD. I began to suspect a much bigger problem -  a hard ware issue.
I took it into the Genius bar the next day. A tech tried to boot my machine to their network diagnostics drive. The drive wouldn't appear on my iMac as an option. Weird, probably an in-store network issue though. He grabbed another Genius. This guy got the diagnostics to run, but that it stated nothing was wrong with the machine. However, even after booting via a thunderbolt drive, the machine would still not unmount the 3TB fusion HD. He said that there were Cupertino engineers that just happened to be there today, and that he would grab one. While I assumed the Cupertino guys are network engineers, I was like, cool, better than nothing. The Cupertino guy, who also was awesome, came over and attempted to unmount the disk via terminal (keep in mind we were booted via the thunderbolt drive). Nope. No good. They walked away for a second and came back stating they think the hard drive needs to be replaced, my original gut feeling as well. I left the iMac at the store awaiting a replacement HD to see if that will fix the issue.
I'm posting this because after I went home and thought about it more, I thought maybe the best course of action is to return/exchange this for one with a SSD instead of a Fusion drive, but I just found out via my account information that I am not allowed to return this machine. Now I am straight up about to panic. Let me stress that every single person I have worked with has been a complete angel, but I now need the advice of the rest of the internet on this one. Even if they replace the hard drive, is it possible there is a larger issue that could strike later down the road, like a lemon computer? Should I be trying to get a replacement? Has anyone ever had this issue? Thanks for any help whatsoever.

Answer 1

If you purchased it directly from Apple (either their on-line store or a brick and mortar Apple Store) and it's less than 14 days old you can return it for either exchange or to get your money back. If it's older than 14 days old, then sorry it's a no-go.