We ran with RAID 6 + a hot spare and a mix of disks, not from the same batch. Again, the alternative is sometimes not even having this. Compared to that it's a pretty good deal, and losing the entire data would be quite inconvenient but not world ending in an academic lab.
And in other labs I've already seen data loss because they messed with their setup in incompetent ways.
You can't always have everything. There is a budget. There are storage needs. You can try to reduce your storage and instead beef up the backups and stuff, but then you can barely do anything and people have to constantly delete their data, and worry about space and that slows things down, generates hostility and conflict between colleagues, and just causes pain in general. You can't see these things from just a technical desirability point of view or what setup would get the most upvotes on r/DataHoarder or whatnot.