"This transforms a vector of arbitrary real numbers into values between 0 and 1 that sum to 1"
Not really, softmax transforms logits (logariths of probabilities) into probabilities.
Probabilities → logits → back again.
Start with p = [0.6, 0.3, 0.1]. Logits = log(p) = [-0.51, -1.20, -2.30]. Softmax(logits) = original p.
NN prefer to output logits because they are linear and go from -inf to +inf.