Frost-Sorc

Ray of Frost: (3×7+4+3+3d8)x2(wet)x2(twincast) -> 62-104(on wet)x2(twincast) -> 166 avg. damage/ action (on two targets) to 83 (on one target). On Bonus action, you can cast Create Water/ Darkness/ Gemini focus damage/ other spells, that are better situationally. Mod: Gemini and Quickspell Gloves to make them once/turn. After doing full-fighter and being easily able to make it deal 50+ damage/hit for no other resources… These caster damages are balanced for no/ minimal (1 sorcery point).

Comparatively, Warlock Eldritch max damage: (2×7+3+1(Spellsparkler)+2(Callous Glow)+1d10+1d8(Spellmight))x3 -> (22-38)x3 -> 66-114 (+1d8 for the 3rd bolts from Spellsparkler instead of +1) -> 66-129 damage/ action compared to our 124-208 damage/ action; at the cost of some preparation required and less target flexibility even with mod, but cold surface is still unmatched control utility.

You can also take a different ‘lock-ish’ path with thief 3 lvl and warrior 2 lvl, still get the elemental affinity from 6 lvl sorc, but have more extra action/ bonus action.
Additional information: Gemini can be combined with Quick Cast for a double ray on one target. However, in normal action Twincast, it only adds one extra ray, and none of them can be used on the same target.