Hoenn's selection of fire types is Torchic, Slugma, Numel, Torkoal and Vulpix, and Slugma is the more common one in the cave you have to go through in the story.
The Chinchou line is something you won't see in GSC unless you fish, and Skarmory is a Silver and Crystal exclusive found in an optional route with no trainer using it.
Johto has an inane ammount of lines that aren't used by trainers, are found just in Kanto, or are incredibly rare in the sole places they are found. AND they are weaker than Kanto Pokemon.
Seriously, Sentret is a rare encounter in the first route (and not at night), while Rattata is even more common in Johto than in Kanto.
Hoothoot is the sole common Johto species, and that's because it is a Spearow equivalent that takes over it AND Pidgey at night. At day it is both Kanto birds everywhere.
Seriously, let's go over the non-starter lines:
- Sentret and Hoothoot already covered.
- Ledyba and Spinarak are early game bugs, version exclusives AND only found at specific times of the day. Weedle and Caterpie are more common. Oh, and they evolved at levels 18 and 22 respectively, into Butterfree/Beedrill tier stuff.
- Chinchou is a common finding if fishing at sea but you won't have any clue it is a thing. Lanturn is quite more solid than stuff like Seaking tho.
- Togepi is a story 'mon, but not really useful in-game, and even if evolved Togetic doesn't really do much.
- Natu is something trainers use, but to get one you need to go explore caves. And, well, no Psychic until level SIXTY FIVE, and Kadabra syndrome.
- Mareep is common, cool and useful (although it coming JUST after the flying gym is a bummer). Sorely missing in Crystal.
- Marill is one of the faces of the gen, but also INCREDIBLY rare in Gold and Silver; you'll fight trainers with it but not find it in the wild. And of course without Pure Power it is uselessly weak.
- Sudowoodo is a story encounter, and a massive downgrade over Snorlax, although pure Rock was a novelty at the time. Still throughly inferior to the very common Geodude.
- Hoppip is common just after the Flying gym, yet makes Chikorita look like a sweeper. Bellsprout is found earlier.
- Aipom is a run off the mill Normal type that is lowkey the thing that may grab your attention for using Headbutt, but still you have to go out of the way to see it.
- Sunkern was literally the weakest Pokemon for 17 years, getting its better moves requires withholding its stone evolution for a long while, and Sunflora is still not too good. Also found in a single area at day.
- Yanma has a 1% encounter rate in a single route. Also quite meh.
- Wooper is a cool bugger that you will likely find, and Quagsire consistently pulls an underdog success performance. Still not quite strong.
- Murkrow is used by a few Rocket Admins and Karen, but it is only found in Kanto. Also a quite weak single stage.
- Misdreavus is literally found ONLY in the final dungeon. No trainer uses it.
- Unown is a gimmick and the focus of an out of the road sidequest, even if they got a movie.
- Wobbuffet is a gimmick found in an optional cave near the 8th gym. No trainer uses it.
- Girafarig is an uncommon encounter in a single route with eh stats yet unique typing. Missing in Crystal.
- Pineco is a rare headbutt encounter in specific trees in specific areas. Forretress is used by Koga, but that's it.
- Dunsparce is a 1% encounter rate in an optional cave near the 1st gym, which also doesn't really bring anything to the table.
- Gligar is a Gold and Crystal exclusive found in an optional route at the 8th gym, 15 levels below the leader, and without STAB.
- Snubbull was also a face of the gen, but 1% encounter rate in a single route, and, even if it does hit hard, it is otherwise quite average before the Fairy type.
- Qwilfish is used by trainers but it has a 1% reel rate in a single route, and Tentacruel is better.
- Shuckle is given to you, but it holds the record for most polarized stats in the game, and the only thing it can do is take hits while you heal something else.
- Heracross is a great 'mon, best bug in the first 2 gens, but it has the same con as Pineco, and nobody uses it.
- Sneasel is used by your rival, but suffers the same issue as Misdreavus in Gold and Silver, which Crystal relocating it to just before the 8th gym. Screwed up by physical/special types, and likely intended to be Gligar's version counterpart.
- Teddiursa and Phanpy are quite solid version exclusives which are also found in the optional route near the 8th gym. Crystal has both of them early in the game, but at morning and with a 1% encounter rate. Phanpy has also no moves pretty much.
- Slugma is the weakest Fire type in the first 2 gens and is a Kanto-only species, even if Blaine uses Magcargo.
- Swinub is heavily used in the 7th gym and is quite common in the cave that opens immediately afterwards, but Piloswine is still not too strong and can't quite use Ice moves.
- Corsola has the same issue as Chinchou, fishing only with no trainers using it. Also can't be reeled at night, and is highly meh in terms of stats.
- Remoraid has the same issue as Qwilfish, 1% reel rate in a single route. Getting Ice Beam in GS is also not enough to make it work.
- Delibird is a gimmick that for some reason was a Silver exclusive. Useless.
- Mantine and Skarmory are defensive version exclusives found at opposite ends of the map, with Mantine in Gold being likely encountered on the way to Cianwood, but Skarmory in Silver being YET ANOTHER optional area near gym 8 encounter. Skarmory is a competitive mainstray but doesn't do much in-game, and there are better waters than Mantine.
- Houndour is a solid 'mon that otherwise has the same issues as Murkrow.
- Stantler is the same deal as Girafarig, but only without the Psychic type, and the route you find it is very short.
- Smeargle is a gimmick found in the same place as Natu, and this one nobody uses it.
- Tyrogue and thus the expanded Hitmon lore is a gift down into an optional cave requiring plenty of HMs.
- Miltank is solid and a daunting boss. Found in a single route alongside Tauros, but they are quite easy to find.
- Raikou, Entei and Suicune are an utter hassle to catch, far less productive than going after the legendary birds in Gen I, but may come far earlier if you are lucky. Suicune in Crystal is pretty much mandatory, but it isn't a tideturning legend.
- Larvitar is a pseudo-legend that comes 25 levels below the other wild 'mons in the final dungeon, the one place it can be found.
- Lugia and Ho-Oh are no gen I Mewtwo in terms of dominance, but getting the version mascot before the 8th gym can do wonders.
