For GSC and to an extent HGSS0, whilst I do appreciate that Steel and Dark types were introduced to counteract the Psychic dominance, I do think the games implemented them poorly when it comes to introducing these types.
For one there aren't many dark and steel types that you can catch in Johto. This includes:
Steel:
- Skarmory (Only get it near Blackthorn city, which is pretty late)
- Scizor (Only acquired through a irl trade whilst holding metal coat)
- Steelix (Also acquired through a irl trade whilst holding metal coat)
- Forretress (Requires getting a Pineco first which has a terrible learnset)
- Magnemite/Magneton
Dark:
- Murkrow (Only can get caught in post-game, and is pretty weak)
- Umbreon (Good defensive wall at the time, and eevee can reasonably evolve if taken well)
- Sneasel (Only can get caught in post-game, and is pretty weak)
- Houndoom (Only can get caught in post-game, but is pretty strong. Would have been nice to have in johto as the only fire alternatives are magmar, arcanine and flareon)
- Tyranitar (Only can get caught in post-game. Considering it's a powerful pusedo-legendary, it'll get an exception).
Not to mention that some of them have pretty learnset, like Skarmory learning Steel Wing at
Level 49 or Steelix getting no Steel moves at all.
On top of which, the Gym fight with Jasmine and the Elite four fight with Karen don't do a good job on showing off their types:
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For Jasmine's fight, it only shows two Magnemite with the same moveset, which is kinda underwhelming when you had to fight Chuck's Primeape and Morty's Haunter. Instead of a second Magnemite, why not replace it with Skarmory to mitigate the Fighting and Ground weakness with a moveset of Leer/Agility/Swift/Steel Wing, or Scizor to mitigate the Fighting weakness and have Leer/Metal Claw/Quick Attack/Focus Energy. Also lol Steelix having Sunny Day to weaken water attacks at the cost of getting cooked by fire moves.
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Karen's team is alright, with Gengar and Vileplume added in to mitigate Dark types' weakness to fighting. I was thinking of adding Ttar to replace Murkrow, but it might make her ace Houndoom look terrible. Best that they could do is to have Umbreon's learnset tweeked to learn Moonlight much earlier so that Karen's umbreon can learn it at level 42, or have Gengar change it's moveset, like Hypnosis to make a terrifying combo with Curse, or learn coverage like Psychic and Thunder to take care of Fighting and Water mons respectively.
Overall I think some of the Steel and Dark types should have been in Johto at a reasonable stage (with the exception of ttar as he may be too powerful) and have some of their learnset tweeked so that they could be useful in-game. But without a good exposure of the two types, a casual player might not really think about them and think they're redundant, like Gen 1 Bug and Fighting.
HGSS does improve their movesets and learnsets, but it is a bit annoying you can't evolve your Magneton to Magnezone.