In my anecdotal experience, Weapon v. Armor adjustments slows down play, which is why it seems to be mostly ignored in systems where it's an optional rule.
There are two reasons I think it was ignored, and one is the one you point out here.
Looking up on a table is slow. But cross referencing two tables is too slow, slowing down play to a crawl.
My solution for this was to not do it, but instead combine the two tables into one before starting play. At most tables, the procedure of play probably looks something like this. A 6th level fighter with weapon specialization and a 17 strength takes a swing at an monster with 2 AC using a +2 longsword. He rolls a 10, adds his bonus to hit from strength, adds his bonus to hit from weapon specialization, adds his bonus to hit from his longsword, and then reports the total. The DM compares this to the needed to hit number on the fighter to hit table to determine if a hit results. That takes up a lot of play time, and if you must also look up on a second table what the modifier for a long sword to hit 2 AC is (-3 IIRC), and then subtract that from the total, the result is really slow both in terms of the 'blink effect' and the separate mathematical operations that go into the calculation.
My solution was a very programmatic one - I cached all the results before playing. For each PC's I produced a 'to hit' table with all of the weapons that they used with all the modifiers from all the normal sources already baked into it. Thus, my process of play involved a player simply declaring an attack and reporting the number on the dice. All the arithmetic and table look ups had been done in a few minutes of preparation before the game, and those tables tended to stay accurate for several sessions (and were easily adjusted). So, in practice, combat played faster at my table which used 'to hit modifiers vs. AC' than it did at other tables I was familiar with, because we avoided the classic D&D problem of trying to add up the fiddly numbers every time.
The other issue, and the more serious one, is that like many of the rules that people ignored, people weren't consciously choosing to ignore the rules, they simply did because they didn't understand the rules and because the rest of the rules didn't integrate the 'to hit modifiers vs. AC' table into the rules well. It was easy to just unconsciously go, "I don't know what those numbers mean, but they must not be important. We'll figure it out if it ever comes up." To really integrate those rules into the game, you had to consciously alter the way you saw AC in a way that even the game's publishers weren't seeing AC. If you stuck to the rules, those modifiers would only come up in the relative rare situation where you were fighting a humanoid wearing a known armor type. I say this was rare, because it often wasn't even explicit in the rules what armor a hobgoblin or an orc was actually wearing. You had an AC, but no way of knowing where it come from. Rarely, and I mean quite rarely, there was a tangential call out to the weapon vs. armor rules in the write up of a monster where it would say something like, "Treat the armor of the monster as if it was chain mail.", without saying why this was important. But for the most part, glancing at a monster manual you'd see neither a reason to use the 'weapon versus armor' modifiers, nor a way to do so if you wanted to.
My solution was to start deliberately breaking 'armor class' into its component parts and reporting it in that fashion for all characters, PC, NPCs, monsters, etc. This was actually the bigger burden. For all characters, you had an 'armor class' that was based on the effective underlying armor, and an 'armor bonus' which was how the number needed to hit that 'armor class' was adjusted up or down. So for example, +1 chain mail no longer simply granted 'AC 4', but granted 'Armor class 5 with armor bonus of +1', or 'AC5(+1)'. Thus, your chain while more protective than ordinary chain, was still effected as if it was chain, and your dexterity adjustment didn't change your armor class but gave you explicitly a bonus to armor class. With that division carefully outlined, the rules came together. Without it, it was entirely unclear what to do with that table in most situations.
Actually, the harder situation, and the one I wasn't fully integrated with prior to deciding I had too many house rules to keep playing 1e AD&D, was figuring out what to do with monster attacks versus PC armor. I for many things just assumed that monster weapons had no modifiers plus or minus versus armor unless they were explicitly a type of weapon, but in the long run I had intentions of producing 'to hit versus' armor tables for natural weapon types (teeth, fangs, claws, talons, tusks, horns, etc.), and/or treating natural weapon types as if they were common weapons (daggers, short swords, spears, maces, etc.)
