Maybe not fair to compare BG3 to BG2 since BG2 starts in the middle of the story. Maybe BG1 would be more appropriate.
And what do we have in Act 1 of BG1? Investigating an iron shortage. Kobold in a mine. Bandits. Some monsters. Some mysterious dreams. Fairly basic stuff and similar to what we have in BG3 Act 1.
Part of what made BG series great was building from that basic DnD starting adventure module in BG1 Act 1 to the super epic stuff in BG2/ToB.
Let's give it time. Right now we only have Act 1 to judge.
I think you are mixing the hero's journey and the setting itself. BG1 started with a classical hero's journey, leading you from humble beginnings to an interesting set up, slowly exposing you to the lore and the world. However, it was so simple that you could have easily changed the setting and the story would not have much differed. Replace Candlekeep with any other library-fortress, replace kobolds with some other small angry creatures, iron shortage is fairly universal (i.e. not FR specific), etc.
The main difference with BG3 is that it throws you in the middle of action dumping all the lore on you from the start. I would argue that BG3 is actually way more Forgotten Realms than BG1 since you are presented with some of its key inhabitants and quirks - Githyanki, Illithinds, Nautiloid, ceremorphosis, which are not present in any imaginary setting out there. But its does not take you slowly through the lore, its throws you mercilessly in the middle of the conflict.
