I think for a security application you want to reduce your exposure as much as possible, and one way to do so is reducing the amount of dependencies in your application. I think a high dependency count is orthonogal to that.
Nitpick: "orthogonal" would mean "independent of"; that is, a high dependency count has no effect on exposure. I think you might have meant "antithetical", meaning "in opposition to".
To be fair, orthogonal just means something that’s at a right angle to another line. I’ve heard people refer to something that is opposite, or an antonym to parallel (or in sync) as orthogonal.
Here it means "perpendicular". A high dependency count is perpendicular to the goal of reducing exposure as much as possible.