BG along with Diablo revived a die'in genre, there hadn't been a noteable release of an CRPG for years until that point, well some people may say M&M was, but meh, it didn't reinvent the genre. CRPG's were well established before this dying off period (see Ultima's, bards tales etc...) but between around 93-97 it was a bleak peroid, where RPG's almost died completely at one point, and what was released was generally extremely poor, BG and Diablo breathed a breath of fresh air into the genre and pushed the bounderies of what found be expected. But it didn't really estalbish the genre, just gave it a jolt.
It's like saying WoW was the first established MMO... Everquest and Ultima Online would be better responses and more accurate, WoW is certainly the first widely popular MMO, but it didn't establish them.
Ok, so Fallout 1 & 2 never existed?
Fallout was the critical success, Baldur's Gate was the commercial success.