There is no such a thing as an eternal ideal; Lancelot himself was the root cause why the Arthurian legends reached its twilight years. By being punished, he wished for the king to understand human limitations, but that never came to pass.
Indeed, Saber is the most fitting Class for Lancelot to be summoned under.
However, Lancelot himself probably feels more than anyone else that it is an irony for him to be a Saber. A noble knight? Don't make me laugh. I participated in the destruction of Britain!
And thus Lancelot is convinced. That the most appropriate Class for himself is Berserker.
Breaking All Restraints - Overloaded Light of the Lake
Rank: A Type: Anti-Army
Arondight - Overload.
Bestowing an overload to the Unbreakable Lake Light, letting the changed magic energy leak out. It is then repurposed into an attack.
This Noble Phantasm is something close to a sword skill, which deliberately refrains from emitting the magic energy that would originally turn into a slash of light, instead releasing it upon cutting at the target.
The blue light of the vast magic energy that overflows from the severed section has been alluded as like a lake.