A bastard sword against a large target does 2d8 damage, 16 max. The strength modifiers don't hit +3 damage until you get into the 18%...in a system that rolled 3d6 in order.
Wait, I thought we were talking about AD&D? Do you think that AD&D used 3d6 in order? Because it didn't. If you used 3d6 in order when playing AD&D, you were not playing RAW. Here we go:
1E PHB, page 9, under
CHARACTER ABILITIES:
"
The range of these abilities is between 3 and 18. The premise of the game is that each player character is above average - at least in some respects - and has superior potential. Furthermore, it is usually essential to the character's survival to be exceptional (with a rating of 15 or above) in no fewer than two ability characteristics. Each ability score is determined by random number generation. The referee has several methods of how this random number generation should be accomplished suggested to him or her in the DUNGEON MASTERS GUIDE. The Dungeon Master will inform you as to which method you may use to determine your character's abilities."
So, no implication of 3d6 in order here. Explicitly states that it's up the DM, and the DMG has several methods listed.
1E DMG, page 11, under
GENERATION OF ABILITY SCORES:
"
As AD&D is an ongoing game of fantasy adventuring, it is important to allow participants to generate a viable character of the race and profession which he or she desires. While it is possible to generate some fairly playable characters by rolling 3d6, there is often an extended period of attempts at finding a suitable one due to quirks of the dice. Furthermore, these rather marginal characters tend to have short life expectancy - which tends to discourage new players, as does having to make do with some character of a race and/or class which he or she really can't or won't identify with. Character generation, then, is a serious matter, and it is recommended that the following systems be used. Four alternatives are offered for player characters:"
It then lists the methods.
Method I is 4d6 drop lowest 6 times, arrange as desired.
Method II is 3d6 rolled 12 times, keep six, arranged as desired.
Method III is roll 3d6 six times for each ability, in order, keep the highest.
Method IV is roll 3d6 in order...and then do it 11 more times, and keep whichever set you want.
[Aside: Gygax's comments about the importance of creating a character that the player can identify with, and being of the race and class the players desires them to be, certainly adds some light on the discussion earlier in this thread.]
Using 3d6 in order, your chance of getting an 18 strength (and therefore exceptional strength if you want to be a fighter) is only 0.46%. That's 1 in 216. Here is the probability of getting an 18 strength using the methods listed in the DMG, assuming you put your highest score in strength if you have that option:
Method I: 9.3%
Method II: 9.2%
Method III: 2.7%
Method IV: 9.2%
So the probability of getting an 18 strength is actually
about 6 to 23 times more likely than rolling it 3d6 in order, per RAW, depending on method used. If you're cool with playing a half-orc (meaning you only need to roll a 17), these probabilities go up dramatically:
Method I: 30.1%
Method II: 20.1%
Method III: 10.6%
Method IV: 20.1%
These are 6 to 18 more likely than rolling a 17 strength on 3d6. But then you'd also have to factor in the maximums in wisdom and charisma, which will reduce the chances of being able to be a half-orc rolling stats in order versus arranging as desired. But I'm sure as bleep not going to do the math on that right now.
A fighter with 18 strength will have a weighted average bonuses of +1.51 to hit and +3.36 to damage.
And while you mentioned a bastard sword doing 2-16, you didn't mention a two-handed sword doing 3-18 for some reason. An average 1E ogre (4+1 hit dice) has 19 hit points. An 18-strength fighter can do up to 21 to 24 depending on strength, average will be about 14 with a two-handed sword.
17% of ogres will have 14 or fewer hit points. So an
average blow from an 18 strength fighter with a two-handed sword will one-shot about one-sixth of ogres. And as established above, although an 18 strength is not the norm for fighters, it is not particularly noteworthy, with a player desiring to create a fighter and not caring about the race having up to a 30% chance of having exceptional strength, depending on the method used. So a 1E fighter one-shotting an ogre is not at all unlikely. It's not the average result, but it's far from impossible. It's not even that unlikely.
[Disclaimer: I cannot guarantee the math is 100% correct here, I did these calculations back-of-the-napkin style. But while the figures might not be exactly correct, they will not be off by any order of magnitude, and the point remains.]