I don't disagree, but you can mitigate that somewhat for that level by taking BB or GFB.
I've done just this but it still feels sucky.
One attack with GFB at 5th level, just isnt the same as swinging that greatsword twice. Moreso on a Paladin thanks to 2 smites being better than one.
Considering a Paladin can dump Dexterity and Intelligence (heavy armor), and still need Strength to wear that heavy armor, I dont see the MAD as being an issue for them to justify the dip. Ditto Bards, and ditto Sorcerers (each for different reasons).
Compare a Paladin (default array, +2 Charisma at 4th) Vuman at 5th level: Str 16, Dex 8, Con 14, Wis 12, Int 10, Cha 16.
If he's dumping Strength to instead focus on Charisma via a Hexblade dip, he's not using heavy armor (or likely even medium armor) due to encumbrance, meaning he needs a good Dex now. His AC is likely worse than that of the above single classed Paladin, he misses out on extra attack, and likely only has a hit bonus of +1 higher than the Strength based single class paladin to make up for it.
He has access to shield, a recharching 1st level slot for smites, and a better ranged attack with EB, but that's really more of a fallback option; his main schtick is getting in someone's face and smiting them dead, which the single classed Paladin simply just does a whole lot better.