What makes Lillie Barro very powerful?

After reading his fight with Shunsui and Nanao, there is something I don't get. How is he considered very powerful, to the point he is matched up against other very powerful characters?

Intangible and can pierce anything also immortal

Was literally going to wreck the Head Captain had Nanao had a super perfect counter ability.

Also, the guy can delete space itself with his shots and go intangible.

@valhallavolund: Intangibility and one hit kill move with X-Axis.

He not really as much powerful as he is haxed

The X-Axis is very powerful. His regen is also pretty good (surviving decapitation and claiming immortality). Though I'm still confused how his intangibility works because his body clearly seems to interact and mold with incoming attacks rather than spatially slip through, and was able to be hurt by Shunsui's reiatsu attack.

Did not know about that part.

This in a nutshell. Nearly immortal and able to kill anyone except for very specific counters

Lille Barro is top 5 strongest in the HST, because of his intangibility and his existence erasure. He easily solos One Piece, and would also solo Naruto and Boruto if not for Genjutsu.

Immortal, intangible, regeneration and ignores durability.

@joshtaku: He erases everything he shoots, it cannot be blocked or tanked, it just erases everything in its path.

The X-Axis

(万物貫通 (ジ・イクサクシス), Ji Ikusakushisu; Japanese for "Piercing Everything"): Lille's Schrift allows his rifle to pierce through anything in its line of sight, with perfect accuracy and without the need for projectiles. It cannot be blocked by any defense.