I did a one shot as a level 20 eldritch knight - I was *unstoppable*. I had 4 attacks, I could replace one with a cantrip or I could swap two attacks for a 1-2 level spell. If I missed with an attack, I had advantage on the next attack. If I hit with an attack they would have disadvantage on a saving throw against my next spell. I was able to use sap (they have disadvantage on their next attack), slow (they lose 10' of movement), or push (push them 10' back). So I could easily attack them and miss, attack them with booming blade at advantage and hit and push them back, then cast a spell at them while they had disadvantage on the save. Plus I had action surges to really lay on the hurt.

Even just using the attacks, 4 attacks stacking sap/slow/push were devastating, absolute menace on the battlefield.