the AC (read: armor type) adjustments for bows are quite favorable if you use them.
Agreed, although two-handed sword is better again. As you noted, how beneficial these adjustments are depends on the sorts of opponents that the GM is using.
But that again puts us in the frame of valuing specialization above all else. If we, for the moment, stipulate that the fighter's ranged ability is significantly inferior to their melee ability (I'm going to disagree later, but for the moment we can stipulate it), but that ranged ability is still better than anyone else's ranged ability (and often as good or better than anyone else's melee ability), then it has value and meaning.
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On the whole, melee does slight more damage than, say, arrows. By the same token, there's a greater chance of receiving damage as well!
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Yeah, but pemerton, you're stacking the deck here. You're saying that if a fighter specializes in melee, he's much better at melee than ranged. Well, yes, sure. But if we're throwing in UA options here, then surely we can go ahead and give a fighter a STR longbow and specialization in that, as well. And/or have him throw that second highest stat into DEX rather than CON.
In UA a fighter can only specialise in one weapon (an OA samurai has the special ability of being able to specialise in both sword (katana) and bow (daikyu)). So a choice will have to be made between melee and bow - and bow specialisation certainly makes a fighter's archery competitive with the melee alternative: looked at through a 4e lens, the UA bow specialist is a precursor to the archer ranger.
I also agree that CON could be sacrificed for DEX in PC building, to opt for a fighter character who is more balanced between melee and ranged combat, but that is feasible in 4e also: build a STR/DEX ranger who alternates between melee and ranged combat depending on circumstances. My feeling is that both builds are somewhat boutique, and probably more likely to be attempted by experienced than beginning players.
The lower hit points and surges of the 4e ranger (compared to a fighter) roughly mirror the lesser hit points of the CON-sacrificing AD&D fighter. The mirroring is only rough, or rather somewhat fun-house like, because the difference between the two 4e PCs will most likely be proportionately greater than that between the two AD&D PCs, at least once surges are factored in. But the flip-side of this is that in 4e the melee-specialised character will use more of those hit points and surges to endure melee, whereas in AD&D I think AC is more important in that respect. (AC gaps across builds really tend to be rather narrow in 4e.)
Moving from the melee-to-missile comparison, to the missile-across-classes/builds comparison, I agree that the AD&D fighter is a strong ranged combatant in AD&D compared to other (non-wizardly) options, although at low levels in dungeon (ie typically close range) environments a dart-throwing thief can be competitive: 3 *1d3 damage averages 6, which is less than the 7 of a bow, but more likely to have a DEX bonus to hit. (The weapon vs armour adjustments for darts tend to be poor at the chain-and-heavier end of the table, though.)
But this is equally true in 4e: only two classes in the 4e PHB have proficiency in military ranged weapons (ie bows): the fighter and the ranger. (The warlord and paladin have to make do with crossbows or thrown hammers and spears.) A fighter in 4e, just like a fighter in AD&D, can take advantage of long range to plink away with a reasonable chance to hit and do some damage - and the fighter in my 4e game, at low levels, carried a long bow for just this purpose.
At paragon tier and above, unless DEX is being pumped, the bow proficiency becomes less and less relevant as the stat and magic-item gap opens up (although inherent bonuses will correct for some of this). But that in itself somewhat correlates to AD&D, where magic item gaps also open up, and mid-to-high level fighters get increased rates of melee attack which open up the damage gap between the two modes.
I know you weren't making a point about 4e, or at least not directly, in your reply. But it was in the context of a comparison to 4e that I made my original remark about AD&D fighter's missile capability, and despite your cogent posts I still incline to the view I started with: a typical AD&D fighter, favouring STR and CON, is notably better at melee than missile, especially post-UA; and that while it is possible to build a bow-oriented fighter, or a mixed-mode fighter, these possibilities also exist in 4e (but under the "ranger" rather than the "fighter" umbrella).
I agree with your earlier post that 4e builds in a relatively high degree of specialisation as a default, but when it comes to mixed melee/ranged combat I think that the STR/DEX ranger is a perfectly viable option for straddling those two modes. The overall play experience shouldn't be radically different from playing a mixed modes AD&D fighter (except to the extent that 4e, in general, is different) with one exception: the mixed mode ranger won't be very sticky in melee. But for a mixed mode character, who is likely to want to play as a skirmisher rather than a "tank", that is probably a net benefit.