The stat contest much be challenging for the roar to train. How much debilitation do you have, and what are you fighting? Are you succeeding?
Area affect roars will teach better because they teach for each enemy they affect.
More advanced roars teach better than easier roars.
"I have no data yet. It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories instead of theories to suit facts."
- Sir Arthur Conan Doyle, Sherlock Holmes