So you admit it: the Fighter is, in fact, weaker than most other classes.
I have said that many times on this thread.
But buffing it (and other classes strongly similar to it) is not okay.
Not unless you buff other classes too. For example, if you give the fighter 3 more feats, the wizard, the bard, the cleric, the Barbarian should all get 3 more feats IMO.
If you give the fighter the ability to use a bonus action to cause a bleeding wound if they hit with a piercing weapon then you should give all classes that ability.
The fighter is still getting the buffs you want if you do this, you just are not leaving other classes behind.
You have all but explicitly said, "The Fighter is no better than anyone else at its specialization, while others can be better at its specialization, or get most of what it does while also doing a whole bunch of other things."
I have actually said it explicitly, back on page 6:
"There is no real comparison. A Wizard is more capable than a fighter IMO because of limited resources. That is how it is, but that is not a reason to give a fighter more feats."
And from this, the one and only so-called solution you will accept is to give all classes 100% identical benefits with no variation.
Not the only solution, but the only solution that involves handing out more combat buffs yes. IMO you should buff them all if you need to buff the fighter.
I have said I would like to see a couple changes to the fighter not related to combat performance:
1. Proficiency in ALL weapons - Catapults, ballista, firearms, laser weapons, the Koa-toa weapons that grapple opponents .....
2. Advantage on any Wisdom or Intelligence skill checks to understand weapons or armor.
3. Fighters bypass all class and race restrictions for magic armor and magic weapons
I would like to see these things added to the Fighter and only the Fighter.
Why? You have already recognized the Fighter—and by extension, the extremely similar Barbarian, Monk, and Rogue—are weak because they critically depend on the Attack action. You have already agreed that spells are simply, objectively a more powerful tool to have, full stop. Why, then, is the one and only valid "solution" to buff everyone equally, so Wizards remain exactly as far ahead of Fighters as they were before? How is that even remotely a compromise?
So that other classes, Wizard, Bard, Warlock and Cleric specifically, don't fall further behind in combat with weapons. Any game that puts those classes way behind a fighter, even when they are built for that role, is a problem for me and will be for a lot of players I think.
When I can't do decent melee damage with my Bladesinger becasue I chose the Wizard class, that is a problem. Being a little behind like it is currently now is ok, being way behind is not ok.
If power is a problem and you want to give something to the fighter and only the fighter to balance it with casters, then give them spells with full caster full spell progression. I would have little problem with that, but I am not for giving them extraordinary martial powers no one else gets above and beyond what they currently have (which is already more than anyone else gets). Doing that would make the game less fun for me and I think it would make the game less fun for a lot of others.
Take the current fighter chassis, add one known spell per level with slots equal to a full caster of the same level. No Arcane recovery, no sorcery points, no channel divinity, no preparing spells, no ritual casting, no cantrips. If you did that the classes would be pretty darn equal I think without having to resort to crazy martial buffs. Further as a build choice a fighter could boost the casting stat (I would recommend Charisma or Intelligence) to be near equal to a caster in terms of magic in the same fashion a caster can boost strength or dex and use subclasses, feats and spells to be near equal to a fighter in melee.
Why is that not an acceptable compromise? If the argument is Fighters are so behind casters because casters have spells and that is not fair then just give fighters the spells!