Husk, 14 bytes

§<ε#εu§m#u
m
<

Try it online!

Husk, 14 bytes

§<ε#εu§m#u
m
<

Try it online!

Explanation

The two short lines are no-ops, since the main function never calls them.

§<ε#εu§m#u  Implicit input, say S = "asasdd"
         u  Remove duplicates: "asd"
      §m#   For each, get number of occurrences in S: [2,2,2]
     u      Remove duplicates: L = [2]
   #ε       Number of elements in L that are at most 1: 0
  ε         1 if L is a singleton, 0 otherwise: 1
§<          Is the former value smaller than the latter?