Tips and details have these 2 lines(direct quote): This skill is affected by the Awakened Will: Optimus passive and is the only skill affected by both the Mecha and G skill bonuses. Potential Bug: Not affected by Awakened Will: Optimus passive
The Awakened Will: Optimus passive description in-game specifically mentions "G transform mode skill" which G-0 Battleroid is not, hence a proportion of the passive is not applied to G-0 Battleroid. Dare to say it is intended and not a bug.