I'm not a Mac fanboy by any means. But SSD write endurance has become ridiculous. Even on a cheap-ish read-intensive server-class 1 TB NVMe SSD (~$300) you get around 1 petabyte total write endurance, meaning you can write essentially the entire contents of the disk every day for 5 years and still be within the warranty. That is orders of magnitude beyond what any consumer is going to subject their disk to.
There is always a possibility that a part of the computer will fail. But if the SSD is less likely to fail than any other random IC on the motherboard, having it soldered on doesn't factor significantly into the failure statistics.
Of course it's super annoying that you can't upgrade the disk size, but that's another point.