So I finally got to see the full episode.
The writers couldn't have made it more obvious that Shirona was going easy on Iris. When Iris was asking for the battle, she talked about how rare it is to be able to battle a pokemon like Gablias and how this would be an amazing experience for her Kibago. Shirona saw her intentions for the battle - to make her pokemon stronger so that she can someday achieve her goal of becoming a Dragon Master - and accepted.
I don't understand why some people wanted Shirona to curbstomp Iris. How in the world would that help Iris in any way? The point of the match was to give Kibago some experience battling a powerful Dragon-Type pokemon, not humiliate it in front of its Trainer and her friends.
This wasn't like the battle with Shinji, where Shinji foolishly thought he could defeat a Champion. Shirona's opponent was a young girl meeting someone she admires greatly, not an arrogant kid who needed to be knocked down a peg. Different opponents call for different battle styles.