The sorcerer and warlock are similar thematically and mechanically because they've always been so. In 3e, they were both alternative wizards with innate, inherited magic. In 4e, they were both Arcane strikers. In 5e, well, people say that the Venn Diagram of Patrons and Origins is a circle for a good reason.The Sorcerer and the Warlock are only similar thematically and mechanically because the designers of certain "gaming generations" who don't explore theme differences much or are swayed heavily by those of those groups.
In each edition, sorcerer has struggled to find its niche, while warlock has basically eaten a few other classes into itself to make its own niche.
Wait, wait wait. Are you saying that the designers of the 3e sorcerer don't get their own creation? The "lets try messing with Vancian casting and see if it breaks the game" class? Maybe you care to enlighten us on how you understand the sorcerer more than the people that made the class?The fact that the Sorcerer has few exclusive spells points that D&D designers since the Sorcerer's creation in 3e, don't get the Sorcerer, and wont try hard to get it unless forced (ie 4e PHB, experimental DNDN playtest).