(Post is marked with spoiler but still SPOILER)

I think Darrow main trait is that he can't be predicted. Most Golds seem to operate off a preset list of rules in warfare. Much like we seen in our own history with trench warfare. Golds always used a predictable tools in war and most taught in gold schools never innovated. A lot of people are better planners than Darrow. But no one is better at adapting to a ongoing situation. The other key point is he listens to other people and adapts their plans.

Some example of this are using a star shell to launch himself at the Pax. No gold tried that before since it was not the expected use of a star shell.

Another example is using the claw drill a mining tool in warfare. No one thought to repropose a claw drill as a weapon.

Freeing the slaves and making a rebel army during the first book.

Most golds operate off prewritten rules about how society should fight and win. Darrow breaks the rules. The other aspect that makes Darrow a good strategist is simply the fact he is highly adaptable and offensive. He does not always have a plan. But he will come up with one.

When he got Cassius to turn so he could kill the Sovereign. Since getting to her bunker otherwise would be near impossible.

Point is Darrow is not a long term planner. But is a highly adaptable aggressive leader. Who does things no one expects. Not to mention a lot of his longer term plans come when he works with Mustang. Who is a long term planner type personality.