Immersion is a mug's game.
What you should be looking for is the suspension of disbelief. And either it works for you, or it doesn't.
Look, you can obsess over just about anything, because ... the campaign world isn't real. Why, for example, don't the maps have bathrooms indicated? Where do the villagers use the bathroom? Where do the PCs use the bathroom????
See what I mean? It's like when you there's a word you use all the time, and then you stare at it until it doesn't make sense anymore to you.
The reason D&D uses a level-advancement system (zero-to-hero) should be obvious, and it's the same reason that D&D is successful as a TTRPG; because players like a feeling of accomplishment. Not just narrative accomplishment, but a feeling of progress! Not all do, and not all to the same extent, but that's part of what makes it a game.
In terms of your own suspension of disbelief, I would recommend not thinking about it too deeply.