I think, that James Horner was just quite pragmatic. Producers needed big amounts of music fast and he did offer them that. There are so many examples of him taking complete passages from classical works. The 3rd of Schumann in the Willow-Theme is certainly one of the most obvious.
And I think, it is all about expectations here. If you want a filmscore to be absolutly innovative, then Horner could cause headaches. Personally, I liked some of his melodies so much, that I was just happy to hear them in other soundtracks, too. Although always slightly changed (e.g. Star Trek II and Aliens). Over the decades, he invented some own themes and repeated those, too. And I did not mind, as long as there was something new to each soundtrack. Especially in the 90's there were some of those (e.g. The perfect storm, Deep Impact), where there was not much innovation. They were mostly boring. But I can absolutly forgive the parallels between Titanic, Braveheart, The devils own, Legends of the fall, Avatar etc. Especially the Titanic-Suite has some awesome moments, that sound like absolute classic Hollywood.
Concerning the comparisons between mainly orchestral composers (like Shore, Horner, Williams or Elfman) and the Remote-Control-Group around Hans Zimmer, I would say, that this is somehow like apples and oranges. The reason for me is the following: The orchestra has developed over hundreds of years now, so the fundamentals for the "orchestral composers", if you want to call them this, are set in terms of instrumentation. You can read about how to balance an orchestra in very old literature already. So the main point for those composers has to be melodies and rhythms and orchestral craftship. The HZ-Guys are more like trying to invent the wheel again. Not completely, but in certain aspects. If you take the Amazing-Spiderman2-Soundtrack for example, you hear so many different sounds involved. And they all have to be balanced well. The orchestra has 2 main settings: european or american (2nd vlns next to first vlns or next to DB). But when you mix synthesizers and orchestra, you always have to think about a new concept. Where do I put which instrument inside the room? And then all those sounds, they create there. This is not easy at all. The classical instruments were developed over such a long time. And the HZ-Guys invent new instruments the whole time. When you hear Horner or Williams scores with synth in them (Amazing Spiderman1, Star Wars), you realize, that they do not feel that comfortable with that. They know, how to balance an orchestra, but I am pretty sure, they don't know so much about Mixing as Zimmer and friends do.
Finally a video of The dark Zebra-Soundset here. I don't own Zebra2, but HIVE from U-He. And I know, there is still a long way to go, until I will be able to craft own usable instruments there, so I just take presets. I find this video so impressive, because here you can see, how much work there has been to do the DK-Soundtracks.