Who told you such idiotic things? By "system stability" it refers to patching exploits. Just look at the change logs between versions and you will see that besides patching exploits there are almost no changes (if any) other than adding new stuff (eg: themes). Game crashes and corrupted saves are nonexistent unless your copy is bad (if pirated) or your SD card is malfunctioning. As for bricks, that's literally only possible if you mess around with the system in a way you aren't supposed to, so WHY would the even bother with that? Finally, there's no such thing as optimization on the 3DS, games are optimized individually and run the same on all supported firmwares.