I always thought Horner stole from himself...a lot. Namely from The Wrath of Khan. Just listen to the Aliens soundtrack. He used the same music for the same scene...When Enterprise pops up behind Reliant and in Aliens when the shuttle arrives just in time to save Ripley and Newt.
Horner uses a four-note ‘evil’ theme that has probably appeared in 30 scores—that’s the one in Aliens and ST2. Years ago I wrote about this and I still believe what I wrote then, which is that the post-production on Aliens was so horrendous he altered his writing style from that point on. He is talented, but he’s lazy. He steals from everyone, as well as himself, and it’s too bad, because he doesn’t have to.