Yeah, Steven was a master of the Steel-type. GameFreak wanted to keep the Pokemon native to their region they're in, otherwise it's kind of weird. It makes more sense for the champion to use their region's Pokemon. There were 9 Steel-types (fully-evolved, that is) during Gen III. Steelix, Scizor, Magneton, Metagross, Skamory, Aggron, Foretress, Mawile, and Jirachi. Obviously, Jirachi is a legendary so they didn't give him that. Steelix, Scizor, and Foretress are native to Johto so there's no sense in them being there. Mawile is pitiful, and is not fit for a Champion's team. That leaves Magneton, Metagross, Skarmory, and Aggron. That is not enough for a team so they cheated a bit and gave him fossil Pokemon and Claydol and took out Magneton.
The same goes with Lance. He had only the Dratini line for dragons. That's one species. They simply didn't have the Pokemon to supply Lance with actual Dragon-types, so they gave him the next best thing: draconic Pokemon.
Alder is different. He doesn't have a main theme or a type that he follows. He's just Alder, simply diverse.