

More drives also equals larger power consumption so you would need a larger battery backup.
It also means more components prone to failure which increases your chance of losing data. More drives means more moving parts and electrical connections including data and power cables, backplanes, and generated heat that you need to cool down.
I’d be more concerned over how many failures you’re seeing that makes you think smaller drives would be the better option? I have historically used old drives from ebay or manufacturer refurbs, and even the worst of those have been reliable enough to only have to replace drives once every year or two. With RAID6 or raidz2 you should be plenty secure during a rebuild to prevent data loss. I wouldn’t consider using a lot of little drives unless it’s the only option I had or if someone gave them away for free.
22:57:20 up 70 days, 16:04, 21 users, load average: 1.10, 1.14, 1.02
Honestly if you were expecting a drive failure in three years, you probably have some other problem. The SSD in my desktop is clocking 7.3 years and I never shut down my machines except to reboot. On my servers, I have run used HDDs from ebay for up to ten years (only retired for upgrades). My NAS is currently running a mixture of used drives from Ebay and some refurbs from Amazon, and I don’t anticipate seeing any issues for at least a few more years.