It's a design problem.
We can't just keep porting all the actual issues of the game onto the backs of players and DMs.
It is not a design problem it is a player making poor build choice problem and then following those poor build choices with poor in-game choices.
I posted earlier about a Drow Fighter I plan to play in a future campaign. On point buy, at 8th level she will have a 20 Charisma and the following spells as single-classed fighter:
Eldritch Blast (magic initiate)
Green Flame Blade (magic initiate)
Dancing Lights (Drow)
Booming Blade (Eldritch Knight)
Friends (EK)
Cause Fear (magic initiate)*
Hex (Fey Touched)*
Faerie Fire (Drow)*
Detect Magic (DHM)*
Protection from Evil and Good (EK)
Shield (EK)
Absorb Elements (EK)
Alarm (EK)
Darkness (Drow)*
Levitate (DHM)*
Blur (EK)
Rope Trick (EK)
Dispel Magic (DHM)*
All of the spells with a * are cast once a day for free except Detect Magic which is at will as an action.
I plan to start with a Greatsword and a Warhammer as my backup and blind fighting fighting style (which pairs well with darkness). I will see where the campaign goes though, maybe I will end up sword and board if we find a good shield or single-handed weapon (recognizing the conflicts with shield spell and Hex) and maybe I will switch to superior technique, defense dueling or something else later on.
She will also have a Raven familiar (unless it dies between level 6 and 8) and proficency in Deception, Intimidation and Persuasion.
That is all on a single-class fighter chassis. I have not played this build before, maybe it will be the bomb, maybe it will be a dud, but on paper it looks darn promising and I can say for a fact whether it is great or it sucks I will have fun playing it.