Board Thread:Theories and Speculation/@comment-35448581-20160502192848/@comment-734582-20160502222607

You're mixing up two things.

First off, one can say that any eye is merely a temporary vessel for that power. As Tobirama explained, the Sharingan and it's various forms originate from the brain. In that sense, dojutsu are just vessels to manifest this brain's power.

Secondly, you're mixing Dojutsu. The Byakugan and Sharingan are two very different lines of Kekkei Genkai. Rinne Sharingan, Rinnegan, Sharingan and Mangekyou are dojutsu of the Sharingan line. Tenseigan, Byakugan are of the Byakugan line. If these eyes can be mixed proper, Kaguya would've done so.

Thirdly, you're mixing the Tenseigan (energy vessel) and Tenseigan (eye power). Hamura awoke Tenseigan and sealed his eyes in the Energy vessel. So the Tenseigan is a real Dojutsu, as real as the Rinnegan. Toneri's Tenseigan allowed him to control the Energy vessel and moved the moon, but even after Hinata destroyed said vessel the moon moved once more via Toneri's Tenseigan.

Lastly, no official explanation exists for the Tenseigan fading. There are many reasons that this could've happened.