Alzrius
The EN World kitten
You're wrong. While it's not nearly as explicit as Pathfinder made it, the idea of the sorcerer having "magic from their bloodline" was present from the beginning:It isn't - you're confusing D&D with Pathfinder.
"Some sorcerers claim that the blood of dragons courses through their veins. It may even be true—it is common knowledge that certain powerful dragons can take humanoid form and even have humanoid lovers, and it’s difficult to prove that a given sorcerer does not have a dragon ancestor. Sorcerers even often have striking good looks, usually with a touch of the exotic that hints at an unusual heritage. Still, the claim that sorcerers are partially draconic is either an unsubstantiated boast on the part of certain sorcerers or envious gossip on the part of those who lack the sorcerer’s gift." -3.0 PHB, page 48.