In this case it only gives 25% more, specifically while sneaking, and since u break out of sneak when you attack, you're basically spending 1 ap to get a 25% bonus on your next attack. For example, consider how you could spend 6 ap. You could do 3 attacks for 300% (3 * 100%) of your damage OR get guerilla and do 2 attacks for 250% (2 * 125%) which is not only worse damage wise, but any proc based status effects will have less chances of landing. This makes using guerilla objectively worse.