you're asking 2 questions here
how do i define it?
and what's the point of it?
the "point" of it, i think, is basically how you described it ... to use these methods that humanity as invented (writing, painting, drawing, performing, music, etc.) to try to arrive at truths about life or the life experience.
as far as how do i define it? well, to start, and mostly easily (since this is what i was disagreeing with in the last post), i DON'T define it as: "a microscopic investigation of (the artist's) life." that is NOT what art is, in this context.
art, first of all, being the product of an "investigation", not the process of it.
secondly, in this context, we're not talking about the life experience but rather the personal details of the artist's life. that is what i am assuming (and, in context, i'm pretty sure that what was meant) what was meant by: "the artist's life."
i define art as (off the top of my head) finished, deliberate works that, in their existence, attempt to represent or explain some aspect of the shared life experience between the artist and the audience.