Well, a lot of that was because Hoenn's Dark types were extremely underpowered in RSE; Dark was still a Special type, and they were all Physical attackers. (Something that also benefited Phoebe, despite her otherwise poor team.) The fact that RSE was when Fighting started to get good (*cough*Brick Break*cough*) also didn't help his cause.
Lorelei, on the other hand, completely reaped the benefits of RBY's mechanics (especially in Yellow, which had better movesets). Fighting types were garbage and had low Special bulk, the only STAB Rock attackers were slow Rock/Grounds who also had bad Special bulk, Fire didn't resist Ice (giving Charizard and Moltres a nasty weakness), Steel didn't exist, Blizzard had 90% accuracy, Psychic was broken (Slowbro and Jynx), and Amnesia was broken (Slowbro). Making matters worse was the fact that the game's
strongest Electric attacker was, itself, weak to Ice (although it, at least, had good Special bulk). And, no, the Yellow Pikachu wasn't going to beat Lapras without extreme overleveling (which wasn't the easiest thing to do back then).
Meanwhile, both Bruno and Agatha were 100% weak to the games'
most broken type, and Lance's Pokémon were all either extremely frail (Dragonair and Aerodactyl) or had a nasty 4x weakness that was easy to exploit (Gyarados and Dragonite). Only Blue provided a real challenge after Lorelei.
Dragon needs more type combos, in general. Anything but Dragon/Flying and Dragon/Ground, please. (And, no, not just on Legendaries and Megas.) Seeing as three of the four "unique" non-Legendary Dragons (ie. Kingdra, Hydreigon, Tyrantrum, and Dragalge) were introduced after Gen 4, I do have hopes that GF is starting to improve on this. (I think the existence of Fairies certainly helps... There's now less of a pressure to give every Dragon a 4x Ice weakness because more things can deal with them.)
That could be interesting. Lance used a Feraligatr in
Stadium 2, so there's a precedent for him having one. I really want Feraligatr's Mega to be part-Dragon just so it can form a "Dragon Starter Trio" with Charizard and Sceptile.