Again, I can tell you it's really not an issue.Just alluding to a fact. Whether LFQW means the fighter is broken, the wizard is broken, or the game is broken may be up for debate (and not the topic of this thread, really) but that it's a mathematical fact of D&D class designs since '74 (the odd blip like Bo9S notwithstanding) is not. It's just a D&D Thang.
It /also/ used to be a D&D Thang that all 6 saves scaled dramatically with level.
In my high level party the Swashbuckler 14 + BM Fighter 6 had Resilient [Wis] as a feat (and would have had Slippery Mind if he took one less level of Fighter) giving him Dex (+14), Int (+7), and Wis (+8) saves. As for other saves he had a high Charisma (+4) and Con (+6) as well (bonuses include his cloak).
He also had Evasion and a few immunities (Poison from a periapt).
He was often Buffed in Saves by the Dwarven Cleric 14/ Paladin 6 (proving +5 to saves when he was near her, or via her Bless) and from the Lore Bard in the party (+1d12 to a clutch save). He also occasionally had inspiration. He also had the Lucky feat.
Any save he missed, would be dispelled or negated with Dispel magic, restoration, calm emotions or similar (we had a Mood Druid 18/ Paladin 2 and FeyTome Warlock 20 in addition to the Cleric/ Paladin, Lore Bard 20 and Swash/ Fighter).
Most casters took Resilient Con for saves. The Paladin had insane saves (particularly with Bless active) and Resilient Con - her only 'bad' saves were Dex which was only +3 (Dex 6, but +5 Charisma) and Int (+5).
She wore a ring of evasion at later levels to counter the Dex saves after a few Disintegrates got tossed her way.
I get the Swashbuckler Fighter wasnt a straight 'Fighter' by any means, but you cant tell me that he didnt get better at saves (along with the rest of the party) along the way.
The only save he sucked at was Strength (+0, including his cloak).
When you look at most classes (and subclasses); they feature a number of immunities, save buffs and defensive buffs to deal with stuff.
Single classed Fighter doesnt have that much (aside from 2 extra ASI for say... Lucky and Resilient - or simple stat buffs and Indomitable) as opposed to (say) a Monk (all saves, re-rolls and a ton of immunities) but on the flip side the Fighter deals considerably more damage than a Monk.
Strengths and weaknesses in each class, encouraging teamwork and a diverse party to survive.
It's a feature, not a bug.