Lv 1 doesn't necessarily mean "clueless nobody who just started adventuring".
DnD allows you to create a character with an already rich backstory, full of a prior life, and that doesn't have to translate into "high level".
For the purpose of "ludonarrative cohesion", it is easily reconciled: Your character simply decides to employ abilities of increasing power just as the threats increase that require them (and as their "XP", as a representation of that, increases as well).
Correct me if I am wrong. But, you are saying that my wizard posses the ability to cast fireball and time stop, they just choose not to because the threat is not high enough? why would they risk their friends, using some minor spells when they fight 30 goblins, when they can end it fast with a single spell?
Well for instance, experienced Wizards (and other powerful adventurers) know that the moment they make things too easily resolved, everyone will come to rely on them alone, instead of growing more resourceful themselves ...;)
But the truth is: as long as the ability to cast fireball is not mentioned in-dialogue, there's no reason to point out that a character should be able to do that if they are that experienced already. There's no need to marry "power level" in game terms with "backstory" in a way that forbids Lv 1 chars from having interesting backgrounds, to have "lived a little" already before getting into this adventuring business.
I'm glad to not be adventuring with entirely clueless teenagers in every RPG. Take games like Dragon Age or Mass Effect: Your companions start as "low" as you do in game mechanical terms, but they had all sorts of lives before meeting you, and lived through some serious shit. The same method can be easily applied to DnD-based games.
