You brought up years, not me.
But it's quite relevant. The 5e rest system, whether a day or the optional week, makes reasonable sense from a narrative perspective. It's consistent. You get enough rest and you're back to fighting form. It doesn't matter whether the next adventure is tomorrow or a year from now, as long as you have sufficient time for a long rest.
Under your proposal, that isn't the case. The only way to recover is to level up. If you run out of hit points and spells halfway to your next level up, you're SoL. Better hope some friendlies can drag you through enough encounters to level you, or you'll remain permanently incapacitated. A bad series of encounters can literally "brick" your party, leaving them with insufficient resources to make it to the next level. It doesn't matter if they rest a night. It doesn't even matter if they receive the best non-magical care for several years. They're done for.
I'm sorry, you seem to be quite fond of this idea, but I just don't see any likelihood that you're going to convince me that this makes sense outside of a purely gamist perspective.