Pikes are incredible powerful. With a partner you can kill any infantryman and cavalry will not even go near you, if they are clever. If you also happen to be an mercenary, you will get some really nice armor that will help you survive many hits and shots.
Of course, Reiters would just ride away from them and fire all the time and enough engineers (1:1 ratio) could blow them to pieces with pure firepower, so in the end, you need a few musketeers or friendly cavalry.