"Jettison some weigh or we'll never get back to Cybertron" - something I picked up last night while watching the Original Transformers movie.
A movie intended mostly for kids & teens, isn't going to follow all the laws of physics or science if scientifically accurate elements are going to get in the way of its (mere) entertainment value. Who here even questioned Astrotrain's statement, when watching the original movie for the first time, or refused to accept the plausibility of it or the entire movie over it?

The "Dark" element here (and the element of weight in space in the 1986 movie) is a small, insignificant element of their respective movies - obsessing on it will just be petty and spoil your own fun (and others) of the other 99% of the Movie.
Enjoy the majority of the movie that makes sense, and ignore the elements that are there for marketing purposes (a foreboding title) or for the purpose of a single plot device.