I have to agree. Solgaleo and Lunala's designs make me think of Reshiram and Zekrom in terms of how robotic they look. Not as bad as Dialga and Palkia though.
Meanwhile the the XYZ trio looked the most organic looking since the Weather trio. Well Zygarde's complete forme did take away that more organic look, it looks like a mecha, which is ironic considering that it's meant to restore the ecosystem.
Solgaleo and Lunala's colouration reminds me a lot of Reshiram and Zekrom, even moreso when you notice Solgaleo and Reshiram have blue eyes while Lunala and Zekrom have red eyes.
The XYZ trio happened to share the same colour triangle as the Hoenn legendary trio - blue, red and green.