I guess it is good that this is about use of language.
Probability and favorability are different things. Yes?
(http://www.oxfordlearnersdictionaries.com/)
favorable:
1. making people have a good opinion of someone or something
2. positive and showing your good opinion of someone or something
3. favorable (to/for someone/something)
good for something and making it likely to be successful or have an advantage
synonym advantageous
probable:
likely to happen, to exist, or to be true
— at best
: under the most favorable circumstances
Originally Posted by
Sienna
It implies probability and an estimation of a "best case scenario" along a spectrum of possible events/results that are considered.
"best case scenario"-most favorable scenario can be least likely, most likely or anything in between so in correct usage nothing is said about probability or it is even implied that probability does not matter.