My... how boastful!
Actually thats not entirely how it is viewed.
We do not, nor have not, ever in the past, and won't in the future believe that everything every different church teaches is wrong. Thats what you are making it sound like, and thats incorrect.
We believe many have lots of good things, and Eternal Truths in them. We believe because of the divisions in the churches, some have this, other might have that, and some have something else thats all good.
None have the whole picture though, which is what Joseph Smith did. He had it all put together for him by God.
Not boastful. Just true. The Church organized by Jesus Christ had to be restored. The Church of Jesus Christ of Latter-day Saints is the restored Church. Until the Gospel was restored to Joseph Smith, nothing the existing church(es) did was "sufficient". If it was sufficient then there would have been no necessity to have the Church restored.