A Useless Class from the Start, So How Did I Become Invincible?

[Global Class Change] + [Power Fantasy] + [Invincible] + [Leveling] + [Comedy]

My name is Su Ze, and I changed into the underwhelming Summoner class.

Long skill windups, insufficient damage, no defensive abilities, high mana costs, and a fragile body...

What am I supposed to do?! Huh? My System awakened?

Long skill windups? The System directly gives me Summoning Skills with no windup.

Insufficient damage? Is damage stronger than a nuclear bomb enough?

No defensive abilities? Why not just tank attacks with my body?

“Where's our Summoner? Protect the Summoner! Don't you know this class is fragile?”

“Uh, he seems to have charged even farther forward than the tanks.”

“???”

An all-around invincible Summoner who can become a pugilist or transform into a swordsman, and serve as both a tank and a support.

Aren't you supposed to be an underwhelming class? How did you become invincible?

(The protagonist is invincible all the way through, with absolutely no frustrating plot points. The blurb doesn't do it justice, so head to the main story for the fun.)