Yup, Tomiyasu was functioning as the assistant series director of XY at the time. He was also the storyboard artist and episode director of The Origin Episode #4 which had some okay-ish battle scenes. Meanwhile, Yamashita already had more experience with being very hands-on through the Openings, Endings, and episodes he would direct and animate on.
Yozakura Quartet: Hana no Uta Episode #1 and
#10, for example, show his ability to director someone else's storyboard and then direct his own (while also providing key animation).