Keep in mind that RAID5 isn’t feasible with multi-TB disks (the probability of failed blocks when rebuilding the array is far too high). That said, RAID6 also suffers the same write-hole problem with Btrfs. Personally I choose RAIDZ2 instead.
What makes you say that? I've seen plenty of people make this claim based on URE rates, but I've also not seen any evidence that it is a real problem for a 3-4 drive setup. Modern drives are specced at 1 URE per 10^15 bits read (or better), so less than 1 URE in 125 TB read. Even if a rebuild did fail, you could just start over from a backup. Sure, if the array is mission critical and you have the money, use something with more redundancy, but I don't think RAID5 is infeasible in general.
* All localized error are correctable, unless they overlap on different disks, or result in drive ejection. This precisely fixes UREs of non-raid drives.
* If a complete drive fails, then you have a chance of losing some data from the UREs / localized errors. This is approximately the same as if you used no RAID.
As for URE incidence rate - people use multi-TB drives without RAID, yet data loss does not seem prevalent. I'd say it depends .. a lot.
If you use a crappy RAID5, that ejects a drive on a drive partial/transient/read failure, then yes, it's bad, even worse than no RAID.
That being said, I have no idea whether a good RAID5 implementation is available, one that is well interfaced or integrated into filesystem.