I don't understand why Cynthia gets so much attention on /vp/ for being difficult. The only reason I can think of is that this board is actually full of underage faggots who played Pearl when they were six.
I stopped playing Pokemon for many years after Gen III. When I started playing again and picked up Pearl, I had no idea what I was doing. I was 100% Karenfag and didn't know/care about physical/special split or stats or pretty much anything. My team was Infernape, Staraptor, Gastrodon, Kricketune, and Bronzong, and I don't remember having any trouble with Cynthia. When I played Platinum later and actually knew my shit, I just set up three Dragon Dances against her Spiritomb with my Gyarados and then OHKO'd all her Pokemon.
I'd just like to ask all those people who have trouble with Cynthia: do you not understand even the basic game mechanics in Pokemon or are your Pokemon always just underleveled as fuck? I'm genuinely interested.