None of the above. I guess "natural wizard" is closest, but only because that's the fluff assigned to the class in the PHB. The Sorcerer is really an odd duck.
In 3E, it was presented with fairly light fluff (which was strengthened, slightly, in 3.5). It was clearly introduced as a variant Wizard for people who wanted to cast spells but not have to deal with the strange prognostication around daily spell selection (i.e. folks like me). Mechanically, it fit that niche extremely well. My group pretty much treated it like a specialist Wizard whose focus was on ditching the spell book. They could study at a college, learn from a hedge mage, etc. The whole "blood of dragons" thing was an rumor that was generally ignored or just gave an excuse for why the character could learn a spell permanently, instead of having to have it re-imprinted every day.
I didn't play 4E very long, but I remember the unified powers system to be a benefit to the Sorcerer, in terms of flavor. It no longer had to use the same tools as a Wizard, so the fluff was allowed to shine. That kinda redefined (or fully defined, not sure) the class as having a non-mechanical reason to exist. Again, 4E really didn't resonate with my group, so the impact on me is pretty mild.
The 5E Sorcerer flails around without purpose. With the revised preparation/slots mechanic for Wizards, the Sorcerer's mechanical niche from 3E has been removed. In theory, the flavor is a natural-born arcanist. Their abilities are supposed to show up somewhat untrained, even if they can be improved with practice. The mechanics really, really suck at representing that, though. Why would a "font of magic", someone with "magical power coursing through" them and "infusing [them] with arcane magic" manifest that as cataloged, named spells that can be reliably replicated by someone who learns how to harness external power from a book? I get the simplicity of saying "as spell XXX", but the whole VSM thing is weird for Sorcerers.
Sorcerers do have the possibility of gaining their power from somewhere other than birth: a fey blessing, "an event in your past", etc. Aren't those the sort of thing handled by the Warlock class? The Warlock class, BTW, has sufficiently different mechanics that it feels more alien than the Sorcerer, despite also having spells.
Actually, what I've done, IMC, is convert the Sorcerer sub-classes to Warlock patrons and ditch the Sorcerer class altogether. The dragon-blooded Warlock is blade-pact, but I'd happily create a "blood pact" for a PC who wanted to actually be born that way. The pact would give an "out" to at least the material components that can be replaced with a focus, as well as saying "Blood-born Warlocks often use words and gestures in their magic, but these take the form of plain-spoken threats and obvious motions (like pointing where a magical bolt should fly), rather than the concrete and precise formulas used by Wizards. Often, the particulars vary from casting to casting by the same Warlock. The magic flows from the soul of the blood-born, with the components being just the subconscious motions of releasing the power." I suppose you could add the same text to the Sorcerer class, but the Warlock class just feels more complete, especially since I don't care for wild mages (leaving only one sub-class to port, from the PHB).
You'll note that there are no references in my opinion to "striker", "tank", etc. I agree with [MENTION=1465]Li Shenron[/MENTION]: Those terms are combat terms and should not be directly tied to particular classes. Some classes will clearly lend them to certain styles of play better than others, but that flows from the class build, rather than informing it. Doing it the opposite way was one of the worst sins of 4E.