Zardnaar
Legend
My current PC started out as a Fighter and multiclassed immediately to Warlock at level 2 and then went back to fighter at level 6 (Figther 2/Warlock 4)
I think the way I am doing it will be more powerful in melee than a straight class fighter at every level except 2 and 7-10
Part of this is my race, feat and invocations. I am level 7 with no extra attack, but I have agonizing Green Flame Blade, so I get a +4 Charisma bonus when Im use it and I reroll 1s on the Fire damage because I have Flames of Phelethegos. So my base Cantrip action does 2d8+8 (1d8+4 slashing + 1d8+4 fire) and if there is another enemy within 5 feet of the first they take another 1d8+8 fire and I reroll 1s on all the fire damage.
In addition to this I playing a Cult of the Elemental Eye Warlock subclass from the Greyhawk adventure's Guide (3rd party). That subclass has an ability called Fire Affinity that you can use once a short rest that lets you add your Charisma bonus to all Fire damage. So when I turn that on I do an extra 4 damage to both the first and second enemy. Additionally this ability causes 4 fire damage to an enemy that hits me in melee (in addition to the 1d4 caused by Flames of Phelethegos).
Just in terms offense I think this is generally outrunning extra attack right now, not every situation but most. Where a single class Fighter would be better is level 7-10 where they have Warmagic and I don't.
Add in 10 damage from Armor of Agathys and Tiefling Hellish Rebuke (with another +4 if I am in Fire Afinninty) my fighter slots which I can use with 1st level Warlock spells like Hex and once Warcaster comes online the shield spell I think at most levels I will be better than a single class fighter.
You know my opinion on being weaker at level 7-10
On a fighter i think I want hex or hunters mark. Ranger dip on EK maybe.
Also want to test the fighter built around shillagh where I can get hex via Fae Touched.