So..only 10 levels later..more than half the game in and near the point where many folks stop playing, the fighter can finally take down multiple of these CR 2 beasies in a turn
And by 'multiple'..I assume we mean that the fighter can take down..2..with action surge and spending resources? Maybe a third if they score a lucky crit and positioning works out?
And by level 20, 8 levels later, that fighter can take down maybe...4 ogres with action surge and resource expenditure? Maybe a 5th with a crit (though good luck getting 5 large creatures positioned such that a Fighter can get to all of them in a turn)
So some classes get access to more and/or better spells every level up. Fighters get the ability to maybe kill one additional CR 2 monster a turn every...4 levels?
At the end of the day, my position is that an easy way to help a mundane fighter without running afoul of the "that's supernatural and I dont want it" crowd is to make fighters significantly more lethal in more circumstances.
The in-world justification is dead simple given that fighters were already assaulting creatures with sharpened and/or heavy chunks of metal. That they should be significantly better at killing things with those sharpened hunks of metal at high levels than low levels would seem likewise narratively consistent with expectations.
Would it need to be tuned? sure Could it be tuned by adjusting both monster hp and PC damage? also sure. Does the adjustment to either monster hp or PC damage need to reflect anything objective beyond the relative threat of one creature to the other, I don't think so, but as a matter of preference, I'd rather keep things consistent over time.
We already have a system that if you budget roughly according to the guidelines the fights take between 3-6 rounds. I don't know what you want or why. A level 6 fighter will be able to single-handedly take out that ogre, perhaps 2 if they spend an action surge ... so what's your point? You want fundamental changes to the game, I don't think they're necessary. Fair enough we have different desires.