In 1st edition AD&D there’s this concept (I know not where) that your level equates to the number of normal men you equal in a fight. A 4th level Fighter Hero is equal to four normal men. It’s a cute approximation and gives a general guideline for power. But it’s actually bogus when you dissect it.
Your toughness in a fight relates to your chance to deal damage, damage potential, chance to resist attack (AC), and hit points. Even if we stick to these the formula doesn’t work out. Related magically is your ability to hinder your opponent or help yourself with spells and your chance to resist hindering by your opponent (saving throws).
Let’s assume anything in the 1E main books (PHB / DMG / MM) is available if you have the starting cash. We roll up two Fighters. Immediately we see differences: one will probably have higher starting HP than the other and so have the ability to last possibly a whole extra round in a fight. Let’s say they both end up with stats without any modifiers and the same average 120 GP starting funds (which is fairly improbable but let’s go with it).
Fighter A: Equip him with Banded Mail, Small Shield, Longsword. AC 3, damage 1d8. Spent 115 GP.
Fighter B: Banded Mail, Short Bow, Spear, and Quiver of 24 Arrows. AC 4, damage 1d6 x 2 (bow) or 1d6 (sword). Spent 109 GP.
Between the two, the second guy will do more damage at range but the first will do slightly more in melee. It depends on the encounter distance, surprise, and the first initiative roll.
What if one of them spent his resources on hiring men-at-arms (expert hirelings, not henchmen)? As a PC he commands these men and so his power includes their power. He might be able to handle the whole dungeon expedition without other PCs!
Fighter C: Hire 10 Heavy Footmen for one month each (2 GP pay, 2 GP upkeep), buy a Spear and Small Wood Shield for each (2 GP) which totals 60 GP for hirelings. Since we have 60 GP left, buy Scale Mail, Small Shield, and Spear for himself. Total spent: 116 GP. AC 5, damage 1d6. 10 hirelings AC 9, damage 1d6 x 10.
Fighter D: Buy 5 Hunting Dogs (cost 85 GP), buy Studded Leather, Small Shield, and Spear for himself. 111 GP. AC 6, damage 1d6. 5 dogs AC 6, damage 2d4 x 5 (and they’re 2+2 HD! Attacking on the monster chart! 16 THAC0!).
This ignores special tactics like buying oil to throw, which does a lot of damage and gets some scientific flak for realism.
I think the combat potential of these four 1st level PC Fighters is different in each case. A and B are similar, but B will win most combats if he gets initiative on the first round. C is dramatically more powerful as a whole and personally only slightly lower AC than A and B. D is somewhat weaker than A/B because of low AC but as a whole his power is amazing.
Of course, we also have M-Us with Sleep who can win a low-level combat if they get initiative but will almost certainly die in melee with any of these Fighters without that spell. And as you gain levels PCs vary wildly in power depending on HP rolls, magic items and equipment chosen, and hirelings / henchmen.
I guess this might sound like a game balance argument, but it’s not. One of the benefits of a game with classes and levels, for me, is being able to compare characters easily. As we all know, each class is different. As the above shows, luck and equipment choices can make far more difference. It’s even worse when comparing PCs to monsters, who may have outlier ACs or special abilities reflected not in HD but in XP value. If anything, XP value should be used to determine difficulty!
This isn’t any better in 3E, with customization making comparison almost impossible. Monsters also vary greatly by type and have an arbitrary Challenge Rating to determine XP value (which is effectively rating difficulty by XP value). Of course, the CR doesn’t match up with HD but it roughly correlates.
So it’s not to say that the game should be better-balanced. It’s taking one stick from the bundle of benefits to using classes in a game.