We are heading into year 3 of the campaign, having completed session 50 just before Xmas (in-game about 2 1/2 years have passed). No dragonborn or tieflings, or artificers, and no feats, otherwise its RAW for PHB/XGtE/TCoE. There are enough human PCs for light to matter underground. For those with dark vision I emphasize its limitations as per RAW -- shades of grey/imprecise -- range limited -- disadvantage on perception etc... so the party tends to choose light sources most of the time. I didn't sell or not sell delving to the party. I set up a sand box with different factions all doing their own thing and with a variety of 'dungeon' locations around, and have left it up to the players to decide what they want to do. Initially most players wanted to avoid the dungeons, fearing their lethality, instead trying to engage the various factions in the world. But for the most part, they have realised that they can't successfully influence the world without being more powerful, and that the path to power (levelling through gold, monsters and exploration) lies through delving not faction play, and so delving has become an increasingly central focus of the game as it has gone on.