You've had far more experience with this stuff than I have. I wonder what your view is on all these NAS RAID boxes and HDD longevity and heat.
I personally never saw so many HDD failures until I started running them inside a small NAS I bought some years ago. I nicknamed it my "drive killer" because I was replacing the things so often. Other HDDs I have in other (non-NAS) machines sure seemed to last much longer.
As for the Deathstar story: I had a similar experience with a Seagate. Inside the NAS, one of the SMART error counts started to rise in a foreboding way, so I replaced it (with an HGST) before it had a chance to die. Then, out of curiosity, I tried the old Seagate in a different non-critical setting (non-NAS) and it's continued to work for two more years. IDK. Too much heat?
If you see this repeatedly with one machine, I would definitely consider that it is the machine which is bad rather than the drives. A power supply may be insufficient to support the peak requirements of the drives, for example. A poor mounting structure might resonate or transfer vibration or shock into one or more drive slots from the environment.
It might seem minor, but just watch this rather old now but infamous video of Brendan Gregg shouting at HDDs causing significant drops in throughput: https://www.youtube.com/watch?v=tDacjrSCeq4
In the past I've used a lot of those Supermicro 5x3" drive carriers and they have really good airflow. This was for storage in servers I built for home use. I wrote up something in 2008 about one I built here: www.tummy.com/articles/ultimatestorage2008/
Faster spinning disks generate more heat and vibrations than slower spinning ones. 15K drives are notorious for needing good environmentals.
My current storage needs are pretty limited, which probably would make SSD attractive. Or we are getting there at least. My storage server right now has 6TB used, and around 1TB of that is backups. If I could get by with 4x 2TB SSDs, I might consider it, just for longevity sake. I'm using ZFS BTW.
However, I can't for the life of me find out whether or not those bays will work with 6 Gb/s SATA. I've been considering putting my Ryzen 7 board into the NAS case to consolidate two systems into one, but I'm not going to go to that effort if I have to get new hotswap bays.
Perhaps heat could have accelerated the process by loosening the material somehow, but it was definitely a design/manufacturing flaw.
Seagates, in general, could always be expected to fail in a 3 year span. Often multiple times. IBM/Hitachi/HGST, especially the UltraStar enterprise line, would basically never fail. Over 20 years and hundreds of discs concurrently running (switching out as opportunity arose), we probably RMAed single digits of HGST drives.
In comparison, while I had a few pockets of Seagate drives that didn't fail (I had 6 in a storage server at home that never gave me problems), we could generally expect 5% of Seagate drives that we had running to fail in a given year. Enterprise or regular didn't really seem to matter.
For us, replacing a drive was fairly expensive, using a limited resource (our time). So we gravitated to HGST almost exclusively.
But: We also did an extensive burn-in process before a drive went into production. Basically: "badblocks -svw" for a week. He noticed that we had some drives that would fall out of RAID arrays, but if we ran badblocks on would never report an error. My theory was that there were some marginal sectors that would bit-rot. Running a week of badblocks would exercise those and allow badblock remapping to remove them from use.
Remember the IBM "Deathstar" 75GXP? We even had good luck with those. I had one of them start freaking out, and I was aware of the "Deathstar" name, so I went to replace it with another drive I had on hand. When I pulled it out to replace it I realized it was HOT. Not in the grand scheme of things, but definitely hot to the touch. I looked up the temp specs and it was clearly above that. The box it was in had 2 5-inch bays that didn't have the covers on them. I covered those bays, turned the machine back on after re-installing the Deathstar, and the drive continued operating for another 3-5 years with no problem. Made me wonder if improper cooling was the source of those reports.