Guerilla tactics can have an effect. The problem is that such tactics are rarely capable of winning a war. Even Mao admitted that the fourth and final stage of an winning resistance movement was the creation of an effective conventional army capable of going toe-to-toe with the regular forces of the opponent.
BTW, you are aware that the loss ratio of guerillas v. regulars is often as high as 20 to 1 and rarely below 10 to 1. In order for a guerilla campaign to be effective, you must have a guerilla force willing to accept such loses over a prolonged period of time.
Yes, a guerilla war is a war of attrition.