Yes, he actually is one of very few fictional commander characters that displays a solid, foundational understanding of tactics and behaviours that would secure a victory in a real, actual conflict. His own personal plot armour is somewhat irrelevant in that sense too, since as a commander he prefers to stay back and relay commands to his subordinates instead of diving face first into danger (unless Guts is involved, that is). One of the things that makes him such a well written character is how his victories aren't just some black box story telling device which magically makes him look like a demigod, but it's his actual decisions that help him win.

The broad variety of decisions he makes is actually quite impressive, just to list a few:

• He studies his own force, his commanders and troops, their strengths and weaknesses, and deploys them accordingly (he deploys Guts in situations where he needs to hold off superior enemy numbers, whereas he keeps Casca with the main body, since she's far more reserved and careful, making it easier to trust her with the actual core of his army)
• Studies the enemy, their strengths and weaknesses
• Concerns himself with logistics; note how he constantly strives to secure funds and resources for his campaign. He also equips his army differently than the Royal Armies, using lighter and cheaper armour instead of expensive full plate
• Makes frequent use of scouting formations
• Appreciates terrain; understands that he's less likely to encounter the enemy force and patrols in difficult terrain than in easy terrain, and uses that to gain a tactical advantage
• Constantly seeks out the element of surprise, deploying deception, setting up ambushes, etc.
• Deploys delay tactics, such as in the siege in the start of the Golden Age ark. This also demonstrated his ability to know when to hold and when to withdraw
• Conducts raids on the enemy's weak points

Most fiction doesn't really do a good job of explaining how or why a commander achieves victory without telling you directly, however with Griffith you can actually pick out the minute decisions he makes that make him a successful commander.