Well, I think we all agree that Devastator is a one-of-a-kind Transformer, don't we?
The case is similar to the Twins' ice cream truck.
One could IMPLY that it would have a robot mode of its own, but it doesn't.

I wouldn't have to.
You can try adding it, but it won't last, and it won't necessarily be me removing it.
Assuming they can transform isn't a valid reason for it to be accepted into Wikipedia.
If assumptions were truth, the movie should have had an Overload or Hightower bots, but there aren't any.
The problem here is that people tend to take as truth for the movie all of the bullcrap Hasbro does with their toys.
I wouldn't even be surprised if Hasbro had asked Bay to have Devastator's components not transform for the fans to stop hassling them about the no-individual-modes Devastator toy.
The fact is, not a single one of Devastator's components is seen transforming, not even in the background, not even suggested to happen off-screen, no nothing.

I'd have to watch the movie a third time, but I don't recall there being THAT much Constructicons.
All I remember is loads of those protoforms that look kinda like Megatron.

 

It is a reasonable assumption that the Decepticon vehicles came from protoforms and it is also a reasonable assumption that Decepticon vehicles can turn back into robots even if we don't actually see them do it in the movie.

In the movie, the only fact is that you don't see Decepticon robots turn into construction vehicles then combine for Devastator.
You only see the Decepticon construction vehicles form Devastator.
To think that these vehicles have no ability to turn into individual robots is of course an assumption and also a very bad assumption given what we know about the nature of Transformers.

In the movie, the starting point for Devastator are the variable number of parts. In the Legends Devastator toy, they have examples of just 2 or 3 constructicons combining. In the movie, 7 unique vehicle designs were used but at least 9 total vehicles were actually used and the maximum number is unknown. So for the movieverse, it seems that a reasonable assumption is that Devastator can be formed from 2 to ? number of constructicons.
In the movieverse, Devastator is not formed by one giant robot who decided to split into a fixed number of parts such as 7 parts.