To say that the LDS is the true Church is to say that, as established, firm, and reliable as other churches may be, the LDS Church is the most established, reliable, and firm church given by God.
That may also be an arrogant claim. If so, we will have to live with it. God's chosen people have lived with that supposed arrogance for millennia, not as special people chosen out of the rest so much as those chosen as priests for the rest of us (Ex. 19:6).
Mormons, too, will have to learn to live among their friends believing that God has chosen to use them as a special vehicle for his revelations and authority and priesthood. The LDS Church is not the only vehicle, but the Mormon testimony is that of all the ways in which God has revealed himself in the world, he has nowhere more fully done so than in The Church of Jesus Christ of Latter-day Saints.