Given the sword and the general gothy vibes I'm kind of thinking this main character is a Hexblade of the Raven Queen and you'll be going after undead.
I cannot think of anything other than Divine Smite that changes the power ceiling that much.
Maybe some edge cases like comboing Path to the Grave with 2014 GWM or Sharp Shooter?
I don't think people are saying that all adventurers have to be from a tragic backstory, just that it's very common for a good reason: if you're already satisfied with your life, you're less likely to leave it behind.
Avernus was my first thought as well, but there's one key hang-up even besides the budget... any campaign, especially one with many eyes on it, has thousands of people who have played it and done their own version of the story. People probably feel pretty strongly about those stories.
Instead...
Honestly it's hard to make generalizations based on anecdotes. My current game I put 60 options on the table for base species, and 3 of the 6 players picked options from the 2024 PHB (Aasimar, Human, and Tiefling). Another picked a 2014 Wyrd Gnome.
We're playing online so the options being...
It does say something about the nature of the setting how rare it is to find a high level character. In some settings like Eberron high level characters are very rare and being level 15 means you're likely the strongest exemplar of your class for leagues... meanwhile in say Exandria, there's an...
So before you start accusing other people of having poor relationships with their DMs maybe look into your relationship with your players because this seems a biiiit unhealthy.