Clockwork Sorcerer, with metamagic, the best skill monkey of the game and more spells than Wizard's prepared spells boring? Ok.
My favorite deadly low level build. I always play it. It do what a mage should do. Fireball, but Super Fireball.
Scourge Aasimar Dragon Sorcerer level 8
Feat: Elemental Adept(Fire) feat, Tough feat and 16 con.
82 HP, AC 16 (21 with shield)
Metamagic: Empower, Quicken.
Action Aasimar's skill
Bonus action: Quicken Empowered level 4 Fireball.
Damage: Final damage 55.
Its one shot against Wizards.
Next turn:
Empowered fire bolt for 18 damage.
Quicken Fireball for 55 damage.
total of 73 damage.
All damage ignores resistence and cover.
Simple, Effective, One Shot K.O and tanker.
Once it is corrected that your initial opening is at 150 ft, and that an empowered Fireball is only 46 damage average after Empowerment and Elemental Affinity/Adept, and considering it's OK to have 3 stats at 16 without taking any ASI...
The story of Young Alfred.
One morning of June, at Foggy Bottom Junior High
Wendy: "What are you going to do after Summer?"
Laeriel: "I am going to enroll at Howard's School of Torchbearing. I hear nice things about their curriculum.
Wendy: "And you Alfred? Going to Candlekeep?"
Alfred: "Sure, I am determined to become a master of magic."
150 ft away, a guy of draconic descent (they were called dragonborn in the past but Foggy Bottom JH insisted on using a more inclusive terminology) started foaming at the mouth, yelling at Alfred.
Alfred: "Who's this raving lunatic? A guy from the football team?"
Laeriel: "No, it's ... I don't know his name actually, he never told us during the year. He's a sorcerer or something... always playing with matches"
Alfred: "I see."
At his tender age, Alfred only had three feats: tough, lucky, and elemental adept (acid). And stat STR 8, CON 16, DEX 16, INT 16, CHA 8, WIS 8. Taking 4 on HP rolls, he got 9+7*7+2*8= 74 HP. Before taking on Chronurgy as a major at Candlekeep, he was a bookish Abjuration Wizard, adding 19 HP of magical ward every morning.
Alfred rolled initiative. Thanks to his +3 vs Young Sorcerer +3, he could have gotten first by being Lucky, and he could have fled, of course. But... what would Wendy and Laeriel think of him? He wanted to impress them and not flee from a lowly Sorcerer! So he used his Luck to get the initiative, threw a Vitriolic Sphere at his opponent (a spell which could do 5d4 (average 14) on a successful save or 10d4 and 5d4 on the next round on a failed save (average 42), for an average total of 28 damage (HP 74 vs 54) and stood his ground. Alfred then gritted his teeth.... And it hurt. Struck by a fireball he was, doing an average of 46 damage (ouch!) or at most 62 (double-ouch!). He really hoped one of the girls would volunteer to rub a soothing balm on his back after that... (did I mention that he was low on WIS?) Thanks for Alfred, the actual damage was much lower since the DEX allowed him to meet the spell DC of 14 75% of the time (factoring his second use of Luck, because he really didn't expect the fight to last more than three round...), so he'd only suffer 29 damage on average, wiping his ward and injuring him (he wondered if it was true that girls liked scars...) (HP 64 vs 50).
On the second round, Alfred cast his second and last Vitriolic Sphere, bringing down his opponent to 22 HP. His opponent advanced to 120 ft, then cast an Empowered, Quickened Fireball and was burned by his own radiant shield. (HP 35 vs 18). He also cast a fire bolt, for an average of 2d10 (12). Alfred knew his opponent had spend 6 SP and was down to 4, so he could not recreate a 4th level slot in this round. He was also glad that no spell had a range of more than 150 ft before spells of the 6th level, and those weren't taught at Foggy Bottom JH, even in A-level courses.
On the third and final round, Alfred was out of luck points and of vitriolic sphere, his most potent spell. He suspected it was of no use to cast a fire spell so he resolved to advance to 90 ft and cast a Lightning Bolt, lacking any serious acid opportunity at level 3, inflicting 8d6 (28) on a failed save and 14 on a successful save, for an average of 21, removing Looney Loner from the fight. His victory was quickly soured when he got detention for reducing another pupil to 0 HP.
(To be honest, this fight lies on who gets the initiative and on who fails first a save, showing that Sorcerer can nova well, but not particularly more efficiently than any other nova-oriented build from other classes).