I'm a well read grad student who's bluntly honest about all things, although I try to be most honest about myself.
The way Galvatron and Arcee talk to each other makes no sense given later revelations. Galvatron, in particular, wouldn't talk to his twin this way knowing what Jhiaxus had done.
Very frustrating, especially since Phase 2 usually integrates history without disrupting it. Later on, though, I think they wanted to make a spectacularly breathtaking reveal - like they tend to do, and it was spectacularly breathtaking reveal - without thinking through the way that Galvatron and Arcee interacted earlier.
Also, I'm now wondering if they'll further deal with this and tie it up on Arcee's side before Unicron, but I doubt it; it was treated as a small moment and I don't think it will be brought back later on before the universe is *sob* destroyed!