To begin with, I know this idea is more suited for MOD than game suggestion.

Anyhow, it's not hard to agree that level 1-4 characters surviving in an environment full of Mindflayers, Red Dragons, Hell, Underdark, not to mention a level 1 archmage NPC, level 5 archdruid... (ridiculous is the only description I can give)

For the sake of (lore) coherence alone, the starting levels should be way higher (or given a choice for player), along with adjusting monster levels to be more "realistic".

The way I see it is the beginning of the game will be filled with NPC/monsters with lower levels (from the bandits to the goblin and gnolls encounters) then their levels would increase to match the player's level (hag and Gith patrol etc.)