Even in terms of core physical ability, there was a wide gap between Yuuki and the demon lord. With Yuuki's kick earlier, Guy left only a single small barrier in place as he tried blocking it, but it didn't even leave a scratch. Look at their respective magicule energies, and it was comical to compare them at all. Guy was on the level of a True Dragon, and for him, it'd be simple to launch another magic spell while Yuuki was busy dispelling the first.