Well due to many broken mechanics in gen 1, many pokemon have been extremely overpowered and I want to share about some of them.
1)dragonite :
In gen 1, the move wrap was extremely powerful due to the enemy not being able to attack back whole wrapped, a common move set to use back then is dragonite while opponent is wrapped, spamming agility then sweeping the enemy team with overpowered moves.
2) Chansey
This is pretty obvious, this is basically a truckload of health, but the important thing is it supposed to have high special defense, but it unintentionally has a high special attack due to the two being combined into a 'special stat' this results in it being able to take and send strong special hits.
3) Jolteon
Flareon sucked in gen 1, Vaporeon is ok but not even close to Jolteon. Jolteon is the best electric type in gen 1 games due to another broken thing being the fact that speed affects critical hit ratio. Although not as fast as electrode, Jolteon is a lot better in all other stats. It has a high critical hit ratio and is definitely an asset in this games
4)slowbro
The special stat. Ah yes, be prepared to hear me talk about this a lot. One word, amnesia. This move sucks, but not back then. It is supposed to increase sp.defense but due to both sp.defense and attack being one star it raises both by two stages. This makes slowbro stacked with amnesia a very op pokemon, that can definitely sweep enemy teams.
5) Alakazam
Psychic was op. Alakazam clearly being the best psychic in gen 1. So I'm using him. Alakazam is the fastest psychic type and has a wide move pool. Psychic was op because dark type didn't exist, ghost and psychic resisted each other in gen 1 but even if they didn't gengar would still be weak to psychic due to poison typing . Bug type was awful in gen 1. With all these factors, Alakazam is a very good pokemon in gen 1 to use for playthroughs and Competitive.
6) Tauros
Tauros is a very powerful pokemon with excellent and balanced stats. Its rather underrated, being in the ou tier in gen 1 but now has dropped down to nu and even ru. It is a beast in gen 1 games. Hyper beam tauros was incredibly popular of a choice in teams. In gen 1 hyper beam will not need to recharge if it knocks out the opponent which it most likely will here. That makes tauros in this scenario, one of the best pokemon that have been degraded over the years.
Lastly on the list, snorlax
Snorlax can gain back all its health easily using rest. It also knows the two staple normal moves in gen 1, hyper beam for the reasons I described and body slam due to chance of paralysis. It can also learn strong moves like earthquake , self destruct and ice beam. Reflect is another move usually put on snorlax.
Anyway these are the pokemon I think are overpowered due to gen 1 mechanics and other features like how they were back then. Gen 1 is a very different game with all these changes we have gone through, these things that make pokemon stated here op were things discarded in gen 2 or slightly later. Anyways what are your opinions? Do you agree or are there any I missed out? If there is please tell me!