no. not at all really. Rayquaza kept the same body markings as Kyogre and Groudon, and they we're obviously connected because of that. Giratina had more differences from Dialga and Palkia, but they still had the metal spiky "mask" things on their heads and bodies, as well as angular markings that matched up with each other.Haven't the third wheel legendaries always been dramatically different from the initial two?
this design for the third legendary doesn't fit the designs of the Zekrom and Reshiram (who have a fairly similar body structure, as well as the tails representing forms of energy)