You're right of course, if only 2 drives were involved. I have 5. ANd one is half the size of the other 4., a leftover from the old server. I have one more usable leftover I could fit in there, but I'll just keep that one as a spare for now, I already have twice the space I had on the old server even with turning on duplication for things I don't really need to duplicate - and this is where it comes in handy. I have 2, maybe 3 classes of data stored on my server - top priority is the "no possibly way to replace this" stuff - mostly photos. Since I have the space, I might enable 3 way duplication instead of 2, plus it is backed up off site. That's actually one of my smaller data sets - I don't have a DSLR shooting monster file size RAW images. Next is the "I could recreate all this but it would take a long time and a lot of effort" which is mostly my music files. I have all the CDs stored away and could go through and rip them all again if it all disappeared, but I'd rather not have to do that. So that is duplicated and backed up offsite. Finally, there is the "it's stored here to be easily accessible from anywhere on the network" not critical stuff that if it suddenly disappeared, I can recreate from any number of sources, including just streaming. Mostly TV and movies. On the old server, I didn't even have this duplicated. I do now, and still have more free space than I had total space on the old one.
Where I stand right now, I have over 12TB free. If one of my 6TB drive fails, I still have, worst case, another 6TB free - the Drive Pool software will automatically add a duplicate for every file that has lost its duplicate due to the drive failure. Like having a hot spare. ANd it will shift data around to make space if it has to, since I'm not using the setting to fill the first disk 100% before going on to the next disk. Like having a hot spare but it's not reserved as only a hot spare like a traditional RAID. Since I added the 4th 6TB drive and the 3TB drive AFTER I had copied the files from the old server, those two drives are mostly empty right now, since the balance option to even out the free space is very low priority right now.
One thing on the new server that will use more disk space than before are my workstation backups. Free Veeam doesn't do dedupe like the built in backup from WHS, so maintaining a similar retention cycle will use a lot more disk space. On WHS, you couldn't place the backup on a duplicated volume, not problem using Veeam for backups, so the backups are replicated.
I've had Windows machines lose power during updates - they've always recovered. Worst one sat there for about an hour, I was preparing to have to rebuild, but it figured itself out. There is a log generated for this, and if you boot to command prompt you can just "fix the file" that it got stuck on. No modern machine is going to be as completely flexible as my old TRS-80 though - don;t need a certain DOS feature? Just delete the file and save some floppy disk space. Didn;t break anything, just meant that feature couldn't be used. In the days of 180K floppies, that was important. No one cares now that you can throw 64GB RAM and a 14TB hard drive in a machine.
I guess I don;t use exotic enough hardware - though my two different model railroad interfaces have to be fairly unique. Only other things I really use besides fairly standard keyboards and mice, and printer, my scope has a USB interface, and I have one of those USB logic analyzers. Outside of PIC and Arduino programmers, that's about it. I've had devices that just plain didn't work, but never had a drive that totally blue up Windows. Not in recent memory, not on my own machines or at any clients.
My work laptop came joined to the company domain, which I don't do, and a bunch of unnecessary stuff installed, so I used the Windows 10 factory reset on it, works very well. Came up like it was a fresh install of Windows 10, without having to reinstall myself (not that it take long from a flash drive, Windows 10, Server 2016, or Server 2019 install in minutes now). The one thing I always see are people running Windows 7 who are forever reinstalling the OS, every 6 months or more. That is something I have never had to do, nor do I see any of our clients doing. When I was regularly playing different games, I was constantly installing an uninstalling software, still didn't have to do that. Slightly more recently, I tried about 3 different EDA programs installed and uninstalled each one on this Windows 10 machine - still don't see a need to restore the system to defaults.
The server, I've even blown away a whole bunch of Windows 10 junk that certainly isn't needed on a 'server' like the Xbox stuff, Mail, Maps, Weather, etc. Yes, you CAN granularly uninstall a whole bunch of that consumer crap. Not that the disk space is critical, I just don't need all that stuff running.