i dont completely agree that the pokemon are bad. a lot of them have bad movesets, like physical sweeping latias, or special sweeping tauros!!
but ive noticed a lot of them have perfect IVs in HP (you notice these things when for example 4 seismic tosses from blissey doesnt quite KO a tyranitar). so it makes me wonder what their IVs are like in other stats - i once got killed by a marowak which must have been jolly with pretty close to max speed IVs.
but i think the thing that kills us, and we often mistake for luck, is
probability. what i mean is this: if i had a battle with you and killed you by using OHKO moves which all just seemed to hit, you would be right to say i was lucky. but if we had 10 battles, and the OHKO moves all hit on the 10th battle, it would just be that the law of averages were asserting themselves. the problem with trying to get a 100 win streak is that somewhere along the way (usually a few times) you
ARE going to come up against some really "bad luck". and you somehow either need (i) a team which can stand up to it, or (ii) a bit of luck yourself.
but my latest streak (101 in the pearl battle tower) was ended by my own complacency. i was just feeling too happy about getting through 100 battles and earning the trophy. i had killed the first two pokes and hadnt lost any of mine and they sent out a slowking. i didnt realise it had nasty plot. so my suicune used rest (it had already used up its chesto berry), and the opponent used nasty plot. at this point i definitely should have switched my blissey in, but i just left it there. two more nasty plots and a few critical hits to go with constant confusion (from swagger) and i was gone. so there was a lot of "bad luck" involved, but i would have been able to win it if i made the correct decisions.