This sounds like the argument: The Melee Warrior's problem is quite simple: "It's always better to be an Archer".
Except it doesn't really work that way.
If you build up your character with a high strength, great weapon fighting style, and possibly some supporting feats like Great Weapon Master, you really want to be in close, and being at a distance sucks. At range, you're stuck with a javelin that you can only attack once with, or worse a longbow that you don't have the stats to use effectively. Even if you're a dex-based fighter, the loss of your fighting style can be a nuisance on the best of days. And in reverse, a ranged fighter
really doesn't want to have to deal with melee combat, since he's built around being at a distance.
Whereas a warlock can usually get comparable (not identical) damage just by backing off and using eldritch blast, with less resource use. I developed a
homebrewery document with some interesting charts that helped recast the entire discussion for me personally. (See document for full discussion / new invocations) I still need to add some AC / HP charts, but figuring out how to do
those effectively is an uphill battle filled with even more guesswork and fill-in-the-blanks than the data I've already done. What's interesting is that, contrary to emotional expectations, blade pact warlocks
can keep up on the damage output level. But they do it, in large part, by spending their resources on hex and the relevant invocations. At the cost of a single invocation, the blastlock has incredible damage output -- probably the best at-will damage in the game once you add in hex.
The underlying problem with the bladelock is that the pact option is making promises it can't support on it's own. The Pact of the Tome gives you some extra spell casting power via cantrips, and the ability to get rituals via an invocation. The Pact of the Chain gives you a familiar, who becomes even
more awesome via an invocation. Pact of the Blade gives you the ability to be functional in melee... and costs you an invocation to
maintain melee relevance in T2, and another to maintain relevance in T3. But it only does this if you also pay in the necessary ASIs, by requiring you to max dexterity.
You wind up pulled in too many directions at once. You really want/need Resilient(Con) & Warcaster to maintain concentration on Hex, since that's how you stay within shouting distance of the fighters with their FS options, which pushes you further back on dex... you need the dex to stay relevant in combat, since damage matters nothing if you can't hit, and it also increases your accuracy... you need charisma to keep your spellcasting abilities up (on the rare occasions you aren't spending them on hex and armor of agathys)...
Mechanically, you have to put a lot more work into a bladelock to make him work than a blastlock. That's OK on some levels, since you're pushing the edges of the narrative space of the class. But it's
not OK on others, because you have a class option hanging around acting as a trap. It implies that this
is part of the warlock's natural narrative space, and the class design should either support that, or the option should have been rejected.