I love the idea of big Constructicons myself. I've had Hercules in combined mode for probably 15 years now and never separated him so the combined mode height is really what matters more to me. I've always envisioned Devastator as being the biggest combiner anyway (whether fiction agrees with that or not) so that would be fine with me if he is a couple of heads bigger than everyone else.
Yeah, I do like the idea that Devestator is a level above your standard combiners. Like in the '86 movie where, since it takes place after Season 2 of the cartoon, combiners on the battlefield have become pretty commonplace, the appearance of Devestator is still treated like a major event. I know there are real-world reasons for that being the case, but in-universe it works.