Nice algorithm!

This is one of the fastest algorithm I tested,(I havent check them all).
I was thinking backwards and checking each character of the string 26 times, you too! but at
least you capped the string to 26, It also seems that checking indexes is faster than checking variables.
Powerful you are master!..

You are returning true inside your for loop, assuming your code aboe was a copy and paste. This would mean you are only ever going to iterate once, effectively only checking for the letter 'a' before returning either false or true.

Good thinking to arrange the order of the letters from least to most common.