I agree. I do not make the claim that the Evangelical Lutheran Church is the "only true church on earth." It is merely the only true church on earth that I am aware of. The Reform Church does confess the five solas of the Reformation, man's total depravity, and unconditional election but errs with respect to the sacraments, the two natures of Christ, and predestination. All other denominations are hopelessly Pelagian.

Romans 16:17 says we should mark those who cause divisions and avoid them. 2 John 10 says we should not receive those who do not abide in the doctrine of Christ. Frankly, given the Reform teaching on "sola scriptura", I don't see how you can consider any known non-Reform denomination to be a true church.