I also did some orchestrations on a couple of his scores. I've had a more creative collaboration with Mark Isham, a good friend. I've worked on a number of scores with him both as synthesist and composer. Every project is different. I look for colors, themes and musical styles that I think will bring out the best qualities in that particular film.
Synthesizers add a lot of energy to a score, which is good for an action film.
But some wonderful scores are done just with orchestra. The best is to blend them both. I have little interest in that. They don't exist without them. A composer's job is no different on an action score than a comedy or lovestory.