Well . . .
Some more thoughts:
The critter (character) with AC 30 is very rare, even at max level. The critter (chracter) with +20 attack bonus is very rare, even at max level.
1st Level
PCs:
- Optimized for attack bonus: +5 attack bonus, but no other neat combat traits or tricks and minimal defense (AC 11 or 12?)
- One trick pony: +4 attack bonus, single special ability, minimal defense (AC 11 or 12)
- Well-rounded striker type: +3 attack bonus, extra manuever/ability (sneak attack?), with decent defense (AC 13)
- Defender trick: +2 attack bonus AC 14, defensive special ability
- Optimized for defense: +2 attack bonus, 15 AC, no other "neat" traits
Monsters (goblins or kobolds):
- Minion: AC 11 or 12, 1 hp, fixed low damage
- Goon: AC 11 - 13, hp ~1.5 * average damage (two hits should kill), fixed lowish damage
- Standard striker: AC 11 - 13, hp 3 * average PC damage (3 - 4 hits to kill), normal monster damage, some attack trait/ability
- Standard soldier/defender: AC 12 - 14, hp 3 * average PC dmg, normal monster damage, some defender trait/ability
- Boss: AC 14 - 15, hp 6 to 8 * average PC dmg, bonus damage, 2 or more traits/abilities
Only the toughest of critters has an AC requiring a roll of 10 by the optimized attack bonus PC, and most critters are easily hit on 8ish or higher by the non-optimized PC. In a similar way, the monsters' attack bonus is in the +1 to +3 range for most critters, but maybe a boss or a special striker (artillery?) has a little better attack bonus or (probably) better damage.
As the PCs level goblins and kobolds can still be a viable threat for several levels, because by say 10th level attack bonus and AC have gone up somewhere between 3 and 5. In the meantime bigger and tougher monsters have slightly better defenses, attacks, and hp, but not some huge level 6 vs. level 1 OMG we can't touch this guy difference.
Continue the flatter math to max level:
PCs:
- Optimized for attack bonus: +20 attack bonus, but very few tricks, and low defense (AC 25 at best)
- Well-rounded striker type: +17 attack bonus, several manuevers/abilities, with decent defense (AC 27)
- Optimized for defense: +15 attack bonus, AC 30, and very few tricks
Monsters (dragons and giants):
- Minion: AC 24 or 25, 1 hp, fixed low damage
- Goon: AC 24 - 26, hp ~1.5 * average damage (two hits should kill), fixed lowish damage
- Standard striker: AC 24 - 26, hp 3 * average PC damage (3 - 4 hits to kill), normal monster damage, some attack trait/ability
- Standard soldier/defender: AC 25 - 27, hp 3 * average PC dmg, normal monster damage, some defender trait/ability
- Boss: AC 27 - 30, hp 6 to 8 * average PC dmg, bonus damage, 4 or more traits/abilities/tricks
The above lists your "max level" (20 or 30) critters. They are the toughest possible monsters in the game. In the meantime, those monsters that were challenging 5 or even 10 levels ago, because the math is flat, are still interesting, if not quite as difficult.
In the above math the worst PC vs. monster situation is defense optimizer at +15 to hit vs. AC 30 boss. Yeah, that sucks for him. But most of the time he's fighting critters that are not max level and are standard critters with AC starting around 24 or so (9 or better to hit). The attack bonus optimizer nails everyone all the time, except the boss and sometimes the tough defenders.
Sneak attack is a trait or trick. Maybe it's attack bonus? Maybe it's damage bonus? I think conditional damage bonus with combat advantage like in 4e.
Anyhow, in this wide range of options you can choose to optimize your attack roll at the expense of everything else, or you can balance your choices.