Downsizing could have been a factor in Studio Series Devastator being smaller, but there is also the idea that the individual Combiner Wars Constructicons weren't designed to a price point, so perhaps Hasbro/TakaraTOMY could afford to make the individual figures slightly bigger. Also, aren't the Combiner Wars Constructicons blocky and hollow in places? The Studio Series Constructicons don't seem to have so many hollow pieces, so they're more compact.