how to roll back to 10.3 with a 5c

The down caret doesn't work in mail. I understand the fix is to downgrade back to 10 something. But that only works with a 6 phone. Every time Apple upgrades one thing it messes up something else. C'mon guys! You really don't have a protocol yet to make sure your upgrades are right before you release them? Or is this just an attempt to get me to buy a new phone? NOT happening!