But I would argue that the basic outline of Peter Parker's biography still makes more sense than that of Cerebus.
After 26 years of publishing, Cerebus was very old and died. He had two marriages and one child.
After 40 years of publishing, Peter Parker is how old? Is he married? Do they have a kid?
How about jobs, how long has Peter been a freelance photographer? We know Cerebus spent his Five-Bar Gate winnings on a tavern, what did Peter do with all the money from his best-selling book of Spider-Man photos? Or the gold notebook?
At least Cerebus was set in a barbarian/fantasy world with magic spells and black towers that grew into the sky [and trips to the moon and Pluto!] Spider-Man is supposedly "the superhero who could be you".
You can disagree about *how* Cerebus' life isn't quite a biography (aardvarks living to an extreme old age, the Three Stooges being allowed to use guns) but for giving us all the parts that go into a life, it does way better than Spider-Man ever did.
Sim was right that most people have their life stories finished by #200 (demonstrated with Cerebus' medallions starting in #4) and the rest is aftermath, there's Melmoth's take on mortality, Jaka's Story which let events happen without explanation, until the Cirinists broke down the door. Who hasn't lived through Guys at one point or another, or seen their life's work turned to shit, as Cerebus learns from Shep-Shep?
Realistic? No. Lifelike? Yes.