I've nothing new in terms of ideas to add after what's been said. Frankly, I think we're good to go with the conclusions already reached in this topic.
However, I'd like to make one case for an offensive Pokemon that's both slow and doesn't have priority. I think the closest example of this is SubTorment Heatran, who without Choice Scarf sits at a Speed point where many common Pokemon beat him easily, but also has a typing that means most attackers will only really carry one move to deal with him. Steelix runs SubTorment similarly in the lower tiers, with either Roar/Dragon Tail for shuffling or Earthquake+Rock STAB or Gyro Ball for its offense.
It's risky to do, and once in you must continually weight your options at each turn, whether to attack, use Substitute (which costs HP) or use Torment for the combo. Pulled off right, it can leave an enemy crippled (especially last Pokemon Choice users). They both have some bulk for it however.
I'm not necessarily advocating SubTorment, although I think it's worth considering. However, that level of risk is manageable for a skilled player without making a Pokemon completely unviable (and note, for Heatran it's made possible because he has all kinds of other options in his arsenal, so that set carries the element of surprise). A slow, mostly frail, yet offensive Pokemon WITHOUT priority (maaaybe just Sucker Punch) is perfectly possible, it'd just be challenging to create (and require help setting up).
I'm a casual Smogoner that mostly frequents the forums - chances are you won't find me on IRC that often. If you want to talk shoot me a PM please, I'm not on every day but I'll eventually reply.