Was this because [Tengai Shinsei] was weak?
No!
It was precisely because [Tengai Shinsei] was too powerful!
So powerful that even Madara Uchiha, its caster, could not withstand it.
But [Tengai Shinsei]'s "drawback in power" was no issue at all for Uchiha Minamoto.
He possessed quite a few ninjutsu whose "drawback was being too powerful."
These included, but were not limited to, [Blaze Release], [Dust Release]... and so on.
Uchiha Minamoto never worried about whether a ninjutsu was powerful enough.
Besides, it was not as though he had no way to circumvent this drawback of [Tengai Shinsei].
When Madara Uchiha used [Tengai Shinsei], he could only crush himself to death along with his enemies.
That was because he had no way to escape the meteorite shockwave's range within the time it took to unleash [Tengai Shinsei].
But Uchiha Minamoto was different.
Whether it was [Divine Lightning] or [Kamui], either could let him completely ignore the physical impact of [Tengai Shinsei].
Even the simple [Lightning Release Transformation Technique] would do!
Uchiha Minamoto did not care about this type of purely physical offensive ninjutsu.
And that was not all.
If Uchiha Minamoto mastered [Tengai Shinsei], it would also be a tremendous addition to his arsenal.
As everyone knew.
The closer a ninja's strength approached the Six Paths level, the weaker the effects of conventional ninjutsu became, until they were completely useless.
Before Six Paths level kekkei mōra.
Even kekkei tōta such as [Blaze Release] and [Dust Release] could not so much as break through its defenses.
That was the difference in mechanics!
But what about [Tengai Shinsei]?
To repeat it once more.
[Tengai Shinsei] had no mechanics, only raw numbers.
How did summoning meteorites count as a mechanic?
Put it this way.
[Tengai Shinsei] was the ninjutsu version of the [Eight Gates