I think I see why they changed artist... the storyboarding of the last one was terrible.
Say what you want about the art, personally, I like this one, but the pacing in the last series was atrocious.
All the GS stories have a thing in common... they take their time and pace events and dialogue well, with the first version of this, there were a lot of things were mushed together to speed run things, the lancer gall was already revealed, which interrupted the presentation of the first characters.
Kumo-sensei must have made his opinion known and demanded someone with better storyboarding.