DonÂ´t believe in the MTBF.
The reliability of the NANDs decrease with every DIE-shrink, so youÂ´re wrong. Endurance-tests show that an older Samsung SSD 830 are able to do over 10x NAND-writes than newer 840 with TLC.
OK, most failures are because Firmware-problems but this is an other szenario. ItÂ´s a thing that that isnÂ´t purposely, but the manufacturers know that DIE-shrinks are not good for endurance
And a PSU -if you donÂ´t buy cheapest things- are not that hard like a HDD/SSD-failure because you donÂ´t loose data
But a external backup ist still the best you can do; even the best SSD/HDD can failure sometimes