Okay, I had a chance to burn through leveling up a melee warlock from the DnD1UA5. Fast tracking 3 warlocks to 20th level is exhausting.
I stepped away from human for this one and went wood elf. I wanted to adapt the fey patron to the UA paradigm but was DM vetoed so I had to keep the fiend patron. I started with the guide background and as a blade pact selected WIS and my casting stat.
Race gave me darkvision (60'), perception proficiency, advantage on charm saves, 35' movement, and bonus spells. The background gave me stealth and survival proficiencies, the magic initiate (primal) feat, +2 WIS and +1 DEX, and cartographer tools proficiency. At 1st level the character looked like this....
STR: 12
DEX: 15+1=16
CON: 13
INT: 10
WIS: 14+2=16
CHA: 8
Cantrips: druidcraft, guidance, resistance, eldritch blast, pact weapon, minor illusion, mage hand
Spells: goodberry, hex, shield, sleep
Skill Proficiencies: perception, stealth, survival, investigation, nature
Weapon and Armor Training: simple weapons, light armor, medium armor
At 2nd level I added detect magic to my prepared spells, devil's sight, and lessons of the first ones (tough feat).
At 3rd level longstrider, burning hands, and command are added for free. I added identify.
At 4th level I took the resilient feat for CON. I added the message cantrip and comprehend languages spell.
At 5th level my pact weapon gave extra attack. Pass without trace, scorching ray, and suggestion were added for free. I added darkness and replaced sleep with invisibility. I added nondetection with mystic arcanum.
I didn't change anything at 6th level. At 7th level I added levitate. I added arcane eye with mystic arcanum.
At 8th level I increased WIS to 18.
At 9th level fear and stinking cloud were free. I added nondetection and dispel magic. I added life drinker via invocation. I exchanged the nondetection mystic arcanum with scrying.
At 10th level I added the friends cantrip.
At 11th level contact other plane was free and I added leomund's tiny hut. I added mass suggestion with mystic arcanum.
At 12th level I increase WIS to 20.
At 13th level blight and wall of fire were free. I added dimension door. I added teleport with mystic arcanum.
I didn't change anything at 14th level. At 15th level I added locate creature. I added visions of the distant realms. I traded the arcane eye mystic arcanum for mind blank.
At 16th level I added +2 to DEX.
At 17th level flame strike and insect plague were free. I added alter self and haste. I replaced nondetection with scrying. I replaced the scrying mystic arcanum with the wish mystic arcanum. I added witch sight. I used wish to cast pact familiar and book of shadows. I used book of shadows to add detect poison and disease and unseen servant, and mending and prestidigitation cantrips.
I didn't change anything at 18th level. At 19th level I took the speedster feat for +1 DEX and +10' movement rate, and added detect thoughts.
At 20th level I took the epic boon of dimensional travel and added +1 to DEX.
The end result looked like this:
AC 19 (+2 studded leather)
183 hp
STR: 12 (+1 save)
DEX: 20 (+5 save)
CON: 14 (+8 save)
INT: 10 (+0 save)
WIS: 22 (+12 save)
CHA: 8 (+5 save)
athletics (+1); acrobatics (+5), sleight-of-hand (+5), (stealth +11); arcana (+0), history (+0), investigation (+6), nature (+6), religion (+0); animal handling (+6), insight (+6), medicine (+6), perception (+12), survival (+12); deception (-1), intimidation (-1), performance (-1), persuasion (-1)
Cantrips: druidcraft, guidance, resistance, eldritch blast, pact weapon, minor illusion, mage hand, message, friends, mending, prestidigitation
1st-level -- goodberry, hex, shield, detect magic, longstrider, burning hands, command, identify, comprehend languages, detect poison and disease, unseen servant
2nd-level -- pass without trace, scorching ray, suggestion, darkness, invisibility, levitate, detect thoughts, alter self
3rd-level -- fear, stinking cloud, dispel magic, leomund's tiny hut, haste
4th-level -- blight, wall of fire, dimension door, locate creature
5th-level -- contact other plane, flame strike, insect plague, scrying
6th-level -- mass suggestion
7th-level -- teleport
8th-level -- mind blank
9th-level -- wish
Invocations: mystic arcanum x4, devil's sight, lessons of the first ones (toughness feat), life drinker, visions of the distant realms, witch sight
A person can squeeze a bit of damage out of the class going TWF for the first 4 levels and then switching to a d10 weapon when extra attack is added. At 11th level switch from hex to haste for the concentration slot because the extra attack is worth more than hex is and eldritch blast plus agonizing blast plus hex beats out the weapon damage without haste.
The 4th EB attack at 17th will still outdo the hasted bladelock weapon damage unless the bladelock has a decent magic weapon. Or invests in feats to qualify for feats that give a minor damage bonus. Or takes 1 level of fighter so that the bladelock can qualify for feats restricted to the warrior group or requiring martial weapon proficiency.
The restriction on heavy weapons against the pact weapon cantrip, changes in feat damage, and restrictions like the warrior group or martial weapon proficiencies costs the blade warlock in weapon support.
Taking a level of fighter for the weapon mastery, martial weapon proficiency, warrior group access, and medium armor / shield training looks like it has some impact.