Why not every 3 levels, wouldn't that allow the fighter to keep ? Or even every 2? I remember in 1e AD&D that fighters got 1 attack/level but only against less than 1 HD creatures (goblins and kobolds mostly it seemed, though there were many others). No playtesting?
Fair question.
Normal progression for a Fighter is: Iterative attacks at levels 6, 11, and 16. 21 would be next, but that's in Epic range and the rules change there. No more BAB progression.
Alternate progression for a Fighter is: Iterative attacks at 5, 9, 13, and 17. 21 would be next etc etc etc...
So the fighter gets one extra attack by the end of his BAB progression. The numbers meshed pretty neatly.
Additionally the fighter gets his/her first bump at the same level Wizard gets Fireball and Lightning bolt, their first big-boom area spells. Again, the numbers meshed pretty neatly.
In a way, though, you could call our last several campaigns the "beta test". We might try a different progression. But four and five interchange so nicely over a 20 level progression, and the results are positive enough that tinkering doesn't really seem to be called for.
We had a player (now departed) whose Cleric had a fighter cohort, and he was disgusted with the cohort's inability to really weigh in on some combats. Seems that the cohort was several levels lower than the PC, due to ECL adjustments, and a 13th level fighter just can't keep up with a 17th level party. But the player swore that: (A) You can't run a relevent fighter at higher levels, and (B) yu can't actually play a Lawful Good in a D&D campaign.
Next campaign I ran a straight melee machine, built straight from the PHB, and another player ran a Paladin. Knowing that a run of the mill fighter type does fall behind on the power curve later on in life, I had mine work to increase his usefulness early and often. To the point where one player challenged his choice of weapon (Spiked Chain), demanding to know what book it came from (PHB), and the group in general became uncomfortable with the Spiked Chain/Improved Trip/Combat Reflexes combo, and had to ask me to tone him down. He swapped the Spiked Chain for a Ranseur (same source, same reach, same damage, just as usable in a Trip, and it freed up a Feat since it's not an Exotic weapon.) Somehow they were satisfied with the change.
As for our Paladin, the disgruntled player was unhappy that the PC wouldn't "take a walk" at convenient times so prisoners could be tortured etc. The same behavior that his own "Lawful Good" PC had tried to get away with in the previous campaign. Yet the Paladin was effective and more than carried his weight in the game.
The point of this is that different people can handle rules and game situations differently. Not just me, but my group has no problem handling stat changes (including INT) the way the rules say they should, but they're not comfortable with power gaming. You seem to favor a different direction, and that's okay.
But if you're going to ask a question like yours on the forum, it's not very good form to dismiss or outright ignore answers that don't support the decision you've already made.