That's a good point you bring up -- it might not be a huge threat competitively, but Norman's Slaking is pretty tough to a team of level 30 Pokemon, because not only is it insanely powerful but it has pretty good defenses too.
I don't find ORAS challenging that is because my team were EV trained beforehand. But Norman still proved to be a great challenge, I can imagine my team getting cleaned if my kids weren't trained. ;)
Oh god yes, this is so true. In my current Alpha Sapphire run, I went against him with none of my team leveled above 30. He managed to KO my entire team except for my Marshtomp (yes he was still a Marshtomp at the time), and it was by sheer luck Marshtomp was able to beat his final Slaking. Slaking is sooo OP, if it weren't for Truant he'd be nigh unstoppable.