Focusing on the “central point” in the midst of a lot of other “unimportant” points is a recipe for Gish gallops because you can claim that any point which has been refuted is an unimportant one. This forces your questioner to keep refuting point after point until you run out of them. That amounts to a Gish gallop.
If the point was important enough to strengthen your argument—and presumably it was or you wouldn’t have used it—it’s important enough that refuting it weakens the argument.
Focusing on the “central point” in the midst of a lot of other “unimportant” points is a recipe for Gish gallops because you can claim that any point which has been refuted is an unimportant one. This forces your questioner to keep refuting point after point until you run out of them. That amounts to a Gish gallop.
If the point was important enough to strengthen your argument—and presumably it was or you wouldn’t have used it—it’s important enough that refuting it weakens the argument.