Scuse me, don't mind me, just-- Pardon me, I'm
Hexblade 1/Fighter 2/Assassin 3/Sorcerer 14
Sorcerer bloodline is a bit up to taste, since there's some good tactical potential with Shadow but any particularly fancy damage shit is UA. For the sake of this demonstration, we'll be assuming Dragon (fire) for the sake of an extra 10 damage.
Splitting stats three ways and going for an Evoker would've been sweet, but unfortunately Overchannel doesn't work on spells cast above level 5...
Yadda yadda advantage/autocrit/hexcurse... We're assuming getting initiative/surprise on an enemy for the sake of this damage calculation. We're also going to assume that, with advantage and whatever, we're hitting every attack (slight stretch, even with Halfling, but makes things much simpler).
Round 1:
Hexblade Curse
8 Scorching Rays (one instance of +5 damage from bloodline)
Action Surge
7 Scorching Rays (one instance of +5 damage from bloodline)
15 rays total, at 2d6 damage per ray. Every hit is a critical, so 4d6 per ray. +6 from curse.
60d6+90+5+5. Average of 210 +100, maximum of 360 +100.
Average will of course get skewed by Empowered Spell metamagic, Elemental Adept etc.
Now, a Paladin mix will still be able to reach noticeably higher maximums, but the
average and
consistent damage from this surprise burn build will actually be higher unless it's a fiendish or undead opponent. It's also got a drastically higher minimum damage.
Of course, neither can get even remotely close to a Twilight Druid magic missile build, but that's UA