Side note, but even if Pinsir was part Fighting-type it still wouldn't have been that good in Gen 1 OU. Gen 1 is dominated by Psychic-types and Fighting was considered a very underwhelming type in Gen 1 because it got absolutely mauled by the dominant Psychic-types in the tier, including stuff like Alakazam, Jynx, Slowbro, etc. Pinsir wouldn't have fared any better especially since it lacked Bug STAB so it wouldn't have had a way to bypass them with a super effective Bug move. Part of the reason Dark and Steel were introduced in Gen 2 was not only to nerf Psychic-types, but also to add value to Fighting-type as an offensive type: Dark and Steel were deliberately made weak to Fighting so that the type had more offensive value.
Anyway, onto two Pokemon of my own:
Let's talk about Heracross in the original GSC, continuning on the trend of Bug-types in the earlier generations. I don't know if you guys have ever used one in-game, but let me tell you, this thing is actually pretty unimpressive in the original GSC. First of all is the fact that it's an extraordinarily rare encounter. You only find it in a select few Headbutt trees in the game, and you have to actively search every Headbutt tree you can find in its route locations to find where it is. It's a lot of time to try to find one.
And then when you actually get it...it's not exactly all that rewarding. Despite having immediately good stats, its level-up movepool is hilariously pathetic and it consists almost purely of Normal-type moves like Fury Attack, Horn Attack, etc. It's not exactly a remarkable Pokemon, and while it's kind of strong early on, it's going to quickly fall off. It doesn't do anything against Morty, it's not all that useful against Chuck, and because it has no good Fighting STAB at all for most of the game, it's not going to do well against Jasmine or Pryce despite being a Fighting-type. It lacks good STAB on both of its types until Level 44-ish with Reversal, which is inconsistent and dependent on Heracross having low HP, and Megahorn at Level 54. Heracross before then is basically a Normal-type without STAB, in which case, why not just use Tauros or Miltank at that point. Not to mention Reversal at Level 44 is its only Fighting STAB since it does not learn DynamicPunch whatsoever, let alone Submission, so that's also another issue with it. Granted, it's probably okay against the Kanto gyms since it can use its Bug STAB and Reversal but getting there is an underwhelming experience.
As for another one entirely,
Talonflame in X and Y. It's one of the coolest regional birds so far, and it was well known for how fantastic it was in Gen 6 Smogon OU and across several VGCs even now. But in-game...this thing is honestly not all that great in X and Y. Fletchling isn't technically bad to start, as it's decent early in the game and does well against Viola. But from there, it just starts to fall off. It has no chance against Grant for one, but the entire Fletchinder phase honestly blows. It's insanely frail and is stuck with Ember and Peck as its best STABs for a great deal of the game, which eventually falls off pretty hard until it get Fly mid-game. It struggles against Clemont and even Korrina because her Machoke has Rock Tomb. Another big problem is that it also doesn't do well against the many Fighting-type trainers in-game because almost all of them carry a Rock-type move. I've recounted several instances where I've tried to use it to take down Fighting-types only for Talonflame to get wrecked by a Rock-type move. In general it just does not hit hard enough either, and it's stuck with pretty mediocre STAB (stuff like Ember and Flame Charge for Fire STAB lol) for a great deal of the game until late in the game. As redemption it's pretty decent against Wikstrom, but it also doesn't stand a chance against Siebold and Drasna, plus Diantha has plenty of ways to destroy Talonflame minus her Gourgeist.
(this is *especially* the case if you're using it with EXP Share off, as trying to baby this Pokemon throughout the game was honestly a pain).
Anyway, onto two Pokemon of my own:

Let's talk about Heracross in the original GSC, continuning on the trend of Bug-types in the earlier generations. I don't know if you guys have ever used one in-game, but let me tell you, this thing is actually pretty unimpressive in the original GSC. First of all is the fact that it's an extraordinarily rare encounter. You only find it in a select few Headbutt trees in the game, and you have to actively search every Headbutt tree you can find in its route locations to find where it is. It's a lot of time to try to find one.
And then when you actually get it...it's not exactly all that rewarding. Despite having immediately good stats, its level-up movepool is hilariously pathetic and it consists almost purely of Normal-type moves like Fury Attack, Horn Attack, etc. It's not exactly a remarkable Pokemon, and while it's kind of strong early on, it's going to quickly fall off. It doesn't do anything against Morty, it's not all that useful against Chuck, and because it has no good Fighting STAB at all for most of the game, it's not going to do well against Jasmine or Pryce despite being a Fighting-type. It lacks good STAB on both of its types until Level 44-ish with Reversal, which is inconsistent and dependent on Heracross having low HP, and Megahorn at Level 54. Heracross before then is basically a Normal-type without STAB, in which case, why not just use Tauros or Miltank at that point. Not to mention Reversal at Level 44 is its only Fighting STAB since it does not learn DynamicPunch whatsoever, let alone Submission, so that's also another issue with it. Granted, it's probably okay against the Kanto gyms since it can use its Bug STAB and Reversal but getting there is an underwhelming experience.
As for another one entirely,

Talonflame in X and Y. It's one of the coolest regional birds so far, and it was well known for how fantastic it was in Gen 6 Smogon OU and across several VGCs even now. But in-game...this thing is honestly not all that great in X and Y. Fletchling isn't technically bad to start, as it's decent early in the game and does well against Viola. But from there, it just starts to fall off. It has no chance against Grant for one, but the entire Fletchinder phase honestly blows. It's insanely frail and is stuck with Ember and Peck as its best STABs for a great deal of the game, which eventually falls off pretty hard until it get Fly mid-game. It struggles against Clemont and even Korrina because her Machoke has Rock Tomb. Another big problem is that it also doesn't do well against the many Fighting-type trainers in-game because almost all of them carry a Rock-type move. I've recounted several instances where I've tried to use it to take down Fighting-types only for Talonflame to get wrecked by a Rock-type move. In general it just does not hit hard enough either, and it's stuck with pretty mediocre STAB (stuff like Ember and Flame Charge for Fire STAB lol) for a great deal of the game until late in the game. As redemption it's pretty decent against Wikstrom, but it also doesn't stand a chance against Siebold and Drasna, plus Diantha has plenty of ways to destroy Talonflame minus her Gourgeist.
(this is *especially* the case if you're using it with EXP Share off, as trying to baby this Pokemon throughout the game was honestly a pain).