Prediction isn't a good argument because they could just as easily out predict your attack and attack back.
Because offense is useless from the inconsistant user's perspective? The point of inconsistant is to stall out until you get enough boosts. If you neglect speed and bulk, you might be able to stop certain counters but you'll end up getting outsped by a lot more and priority will hurt much more.
That is only true before +2. There is only marginal damage change from Min hp/min def and max hp/evenly spread defenses after +2 (you might as well go max def then since there is really no point in special defense most of the time since it takes max max to avoid even being 2 hit koed after a +2 boost from Zapdos and Roserade if they hit you). An 8% change from 352 and 218 vrs 291 and 186. What this means is that Mach Punch can break substitute even with +2 (with Guts, without Guts, Mach Punch couldn't do much diddly squat either way). But why would they if they expect to need to do it with Drain Punch?
Also, max special attack can potentially 2 hit ko Mushroom and Roopushin (almost a ohko on Shroom with Icebeam/Flamethrower and is with Stealth Rock while it ohkoes none special defensive invested Roopushins with +2 boost) while no special attack can't. Also, you can maybe 3 hit ko (max special defense/max special defense might barely survive) Burungeru with +6 resisted Flamethrower/Icebeam (you'll force it out of Recover before you run out of pp) with max special attack while it will pp stall you to death without Toxic with none. So it could, potentially with enough satk boosts kill it eventually. Needs to avoid Taunt though. You also kill Latios/min-min Latias/Zapdos/Roserade ohkos with +2 Icebeam with Max over no special attack investment. You also still almost ohko kill Toxicroak if you went with Icebeam over Flamethrower with +2 while it won't with min special attack. I can see why min special attack might choose Toxic because it loses some useful ohkoes without investment
I guess it might help to be able to outspeed Shaymin/Darkrai. But you would rather have the evasion since even if you outspeed it, with no special attack, you can't ohko Darkrai with Surf while you can with max Timid (or Modest). No special attack means you couldn't 2 hit ko Shaymin with just Surf (so you'll need Flamethrower/Icebeam then which it wouldn't have according to you) while could with investment and Deoxys +spd nature will always outspeed you even after +2 no matter what nature you run. There is a large change in ko potential from no special attack to max, hence the reason why I like the more offensive attacking versions.
It is kind of like Gyrados, offensive and defensive variants (kind of). One straight out attacks with massive power after Dragon Dance while the other hopes to get multiple boosts with invested defenses (except in this case, both Octilleries get multiple boosts each and every round). The offensive kills more stuff period at the opening while the defensive one could as well after a boost or two and even more effectively. Except in this case, it seems reversed where offensive seems to work more efficiently (in my opinion) although the defensive one could make a sick staller. The only problem is that the defensive one gets stalled to death by Burungeru/Tentacruel/Toxicroak while the offensive one doesn't (since he kills Toxicroak and could kill Burungeru/Tentacruel eventually after +6 boosts assuming no Hail/Toxic Damage on it and maybe Taunt). And he could kills other pokemon that really hurt it that the defensive once couldn't (Breloom, Shroom, Cloyster, Roopushin, Latios/Latias with Refresh, Zapdos...)...
Hence the reason I personally prefer the offensive variants and after +2, there is only a marginal %change really (almost all the things that could break your sub at +2 still would with defenses invested or not except maybe Guts Roopushin Mach Punch or maybe unboosted Cloyster Rock Blast.