How can a Muslim believe that something is better than Islam? That would be a walking contradiction.
Spreading Islam is the duty of every Muslim and canon of the faith. By this definition, Muhammad and his companions too were Islamists, no? They dedicated their lives to make sure that Islam reached as many people as possible and achieved miraculous victories on their path. All prophets and messengers struggled with communities in order to convince them that Islam was the best for them.
There is no political Islam. Just like there is no spiritual Islam or scientific Islam. It's alpha and omega in a Muslim's life and governs every aspect of it.