A thing on timelines here: The two main storylines in TLJ start at different times. The escape storyline starts a week after the events of TFA; the Ach-To storyline happens immediately after the events of TFA.
The bomber: People complained about how the bomber thing was unrealistic because there’s no gravity in space. That pedantry is inaccurate. The bombs fell due to the gravitational force of the Star Destroyer underneath the bomber. This is the same reason that Star Destroyer falls into the Death Star in ROTJ.
I read in the visual dictionary that the bombs used magnetic tech as well.
Yes, and that is unnecessary. The artificial gravity within the bomber is enough to give the bombs an initial velocity once they are released to propel them towards the target, as Mrebo already pointed it out.