WHen I had the game like 4 years ago I hacked it and had all the pokemon lvl 100 or something like that. :P And I would say the weird long pokemon is the best. :P

do the 99 rare candy cheat

... Any Pokщmon over lvl 70 should be able to do it with ease.

Otherwise, lrn2ply. I plan on fighting them with my team at about lvl 45-50. No legendaries.

And I doubt I'll find it in the least bit difficult.

If you're really stuck, take a sweeper, like Scyther, Weavile or Gyarados.

"it must be due to human error, this sort of thing has cropped up before and it has always been due to human error"

i did a speed run the first time i played through that gaem and beat the elite 4 with an infernape at lvl 50, everyone else in the 10-30 range, and without using dialga. just get one strong guy and 50 or so revives. if your main guy faints throw one of the other 5 dummies in there, use a revive on your main guy, and send him back out when the dummy faints(always works for me). if even this fails then it must be the problem i listed above:P

^^^^^^^^^NOOB!!!!! Just joking, but my breloom ownes the entire elite four without any items, its level 73, and it knows spore/Focus punch, the best combo ever, along with stone edge and seed bomb to back it up. it holds a toxic orb. EV training helps alot. you can get stats raised by 14 sometimes after ev training.