I want to play a Dragonborn Sorcerer.
Isn't sorcerer a bit underpowered in 5e? Specially regarding archetypes?
No, the main complaint about sorcerers is there lower Spells known list which is 15-16 spells by level 20 depending on subclass. But between Metamagic and the ability to get an enhanced effect from casting spells in a higher spell slot it's functional more spells then it seems like.
For example a Divine Soul Sorcerer (who can chose from cleric spells as well as Sorcerer spells for spells known) can cast Cure Wounds in every single spell level, each higher slot used heals more damage, so in 3.5e terms that is like having Cure light wounds, Cure moderate wounds, Cure Sever Wounds, and more. It's the equivilant of have 9 healing spells. Then you add in Metamagic, so you can cast for example 1st level Distant Spell Cure Woubds, 2nd Level Dosint Spell Cure Wounds, ect..., as well as Twin Spell and Sublte Spell metamagic versions, as well as Empowered Healing (technically not metamagic, but works simularly). And you can do this most damage spells as well, like Guided Bolt, Chromatic Orb, Fireball, ect..., and various other spells, like Command spell targets an extra target for each higher spell level of the slot used, by using a 6th level Major Illusion becames functionally Permanent Illusion, and add in either Subtle Spell or Distant Spell metamagic makes it even more interesting.
Plus a bunch of at will cantrips that you can apply metamagic to.
If that is not enough you have subclass based magical powers, such as Shadow Magic's at will 120' bonus action teleporting, Hound of I'll Omen, and Shadow Form, the Divine Soul and Dragon Blooded's at will wings, Storm Sorcerers at will Flight, and so on.
And if THAT isn't enough you can get more spells via feats, like Ritual Caster: Wizard allows you to get the Wizards ritual spells (15 spells) in a ritual book, which you can apply metamagic too, Magic Inniate, certain Racial Feats, multiclassing, and certain races inniate magic.