Branduil said:
It's not really a question of viable vs. not-viable. The question is, is an 18 in your primary stat more valuable than a more even distribution? I would say, the vast majority of the time, the 18 will prove to more valuable in the long run.
Assuming you make it to the long run.
Sometimes, getting that 18 will cost you - dearly. To get it, you might have to dump a stat that you NEED in order to survive.
The question isn't (or shouldn't be): "is the 18 attack stat character a good option." The question is whether the character without an 18 in his primary attack stat is viable.
Now, even Nifft has admitted that there are characters for whom it's true, like the Dwarf fighter. Racial abilities they get make the combination viable, even when the stat bonuses are less than totally favorable.
Let me pull out an example: a human ranger. We're told his primary stats are Strength, Dex and Wisdom. And obviously, with any character, Constitution makes a good choice (more hit points and healing surges). Our human can get a +2 benefit to any one attribute. Conventional wisdom says we either:
a) Focus on two-blade powers and make strength an 18, or;
b) Focus on archery powers and make dexterity an 18.
But is that the best choice? If we shoot for an 18, we end up with only 2 other attributes that are better than a 14. Some of the options:
18, 14, 13, 12, 11, 10 (default array and +2 human bonus)
18, 14, 14, 12, 11, 8
18, 15, 13, 12, 11, 8
18, 16, 12, 11, 11, 8
18, 16, 12, 10, 10, 10
There's no way to get a good strength, and dex, and wisdom this way and have anything left over for Con. Alternatively, if we shoot for a 17 or 16 as our high stat, we can pull off some interesting math...
17, 16, 13, 13, 10, 8
17, 15, 13, 13, 12, 8
17, 15, 14, 13, 10, 8
17, 14, 14, 14, 10, 8
16, 16, 14, 12, 11, 8
16, 16, 15, 11, 10, 8
16, 16, 14, 13, 10, 8
16, 15, 15, 13, 10, 8
16, 15, 14, 14, 10, 8
For someone wanting a balanced character, there's a lot of viable builds there. Like this one:
Gareth
Human Ranger 1
Init: +5
Perception: +7
Defenses: AC 18, Fort 14, Ref 15, Will 13
Hit Points: 30
Bloodied: 15
Healing Surges: 7 (7)
Attacks:

(Standard, At-will) Longsword +5/1d10 +2

(Standard, At-will) Longbow +5/1d10 + 3
Twin Strike (Standard, At-will)

Longsword +5/1d10, two attacks
Twin Strike (Standard, At-will)

Longbow +5/1d10, two attacks
Hit and Run (Standard, At-will)

Longsword +5/1d10 + 2, plus if you move in the same turn, leaving the first square does not provoke an OA from the target.
Evasive Strike (Standard, Encounter)

Longsword +5/2d10 + 2, plus shift 3 squares before or after the attack, or;

Longbow +5/2d10 + 3, plus shift 3 squares before or after the attack.
Hunter's Bear Trap (Standard, At-will),
Hit: Longsword +5/2d10 + 2, or Longbow +5/2d10 + 3, and target is slowed and takes ongoing damage 5 (save ends both).
Miss: Half damage, and target is slowed until the end of your next turn.
Feats: Toughness, Quick Draw, Lethal Hunter.
Skills: Nature +7, Perception +7, Stealth +7, Athletics +6, Acrobatics +7.
Class Features: Hunter's Quarry, Two Blade Fighting Style, Prime Shot.
Str 15 (+2)
Con 13 (+1)
Dex 16 (+3)
Int 10 (+0)
Wis 15 (+2)
Cha 8 (-1)
Gear: Adventurer's Kit, Hide Armor, Longswords (2), Dagger, Longbow, Arrows.
How is this not a viable character? What does an 18 buy me? +1 to hit and damage? Thanks, but with a +5 to hit on all my attacks, I think I'll take my chances. Alternatively, I could give up a point each in Str and Wis (wouldn't lose any bonus) to get an 18 Dexterity. Then, my dex attacks would be much better, but my strength and wisdom would be worse.
Yes, I admit it's better at Level 1, but those 15s mean Str and Wis can each be bumped to 16 sooner rather than later.
I guess I have a problem with tagging the character's entire "effectiveness" to how often he hits in combat (and moreover, how well he does that
at 1st-level). I just think people are assigning an awful lot of value to a small to-hit bonus and deciding that anything else is therefore "sub-optimal."
Plenty of things matter. That extra healing surge from having a 12 or 13 Constitution instead of a 10 is huge. Alternatively, I could take that extra 2 points from cutting Wis and Str to 14 and give myself a 14 Con instead of an 18 Dex. Which is one
more healing surge.
That's occasionally going to come in much more handy than a measily +1 to hit and damage. IMO only, of course.
If it were all about the two-hit bonus, then all rangers should take two-blade style for the better attack bonus. Longswords give a proficiency bonus of +3, whereas longbows only give +2.