Yes, Careful Synthesis does have a higher loss of durability when it fails, but you can use Tender Touch to guard against durability losses. Alternatively, you could use Fullfillment to increase the rate of success. The same can be said for Rapid Synthesis, in which case I would recommend using Masterpiece to increase it's rate of success. And then, of couse, there is Preserve which helps to maintain favorable synthesis conditions If you have Perfection you can guarentee the success of your next synthesis action and thus shave off time via rapid synthesis or gain a little bonus exp via careful synthesis.
Now, I didn't say there was no reason to use Careful Synth. That's besides the point since the title of this thread is :
"Give us a reason to use anything but standard while synthing!"
and that's exactly what I've done. I've given you a reason to use cross class abilities to ensure and increase the success rate of your Careful/Rapid/Standard Synthesis Actions, particularly if you wish to successfully grind on a recipe that is 5+lvls above you. What you say about botching even more on a synth 5+ lvls above you is not necessarily true. Did you ever happen to come across this thread? It's an oldie, but a goodie:
You can see he botches on average twice after a string of 6 or 7 successful synthesis, and even the botches yield 300exp on occasion. Furthermore I don't think he was using a Grand Company Manual either, which would have had the effect of netting him over 900+exp per successful synthesis. All it takes is a few mid lvl crafting abilities, the right gear, and the judicious use of those abilities on a recipe high enough above you:
But those lvl 36 abilities are by no meanss necessary, as the OP of that image was doing this only with lvl 10 abilities from what I understood. Now if that isn't reason enough to use something other than standard synthesis even once every three actions, then I don't know what would do the trick.
You might want to check out Twinkles' Crafting Guide while you're at it.
I hope that helps! Happy crafting!