...You do realize that every generation past Gen I has these "rip-offs" it is part of the overall design of the series. On top of that, Generation III brought more unique Pokémon than did Generation II or even IV.
All the ones I can think of out of my head:
Slaking was a rip-off of Snorlax. Late-game normal types with some restraints, but lots of power.
Beautifly was a rip off of Butterfree, with Silcoon and Cascoon being rip-offs of Kakuna and Metapod, and Wurmple as a rip-off of Weedle and Caterpie. They were all early-game bug types that evolved fast, based on the same concepts.
Ralts was like Abra, because when you raised it, it didn't know any damaging attacks, so you had to use other techniques (Exp. Share or switching pokemon). They were psychics that were hard to raise but became powerful.
Tailow was much like pidgey, they were both early-game flying types that evolved into a good bird pokemon (Ash even had both in the anime). I know that Hoothoot and Starly were rip-off too, but Hoothoot could learn some psychic attacks, and Starly learned some unique things.
Skitty and Delcatty served the same purpose as Meowth and Persian.
They had Cradily and Armaldo, which essentially replaced the old fossil pokemon.
There was bagon->shelgon->Salamence, which was a Gen III version of Dratini's line.
Spheal->Sealeo->Walrein were a replacement for Seel and Dewgong.
Pulsle and Minun were like two Pichus designed for showing off the double battles.
All of these pokemon had to be made because Gen III wasn't compatible with Gen II, and many pokemon from Gen II and Gen I weren't available in Gen III. So instead of coming up with new pokemon ideas for new content in the pokemon games, they just ripped off of a bunch of the Gen I pokemon so people could still have those early-game butterflies, or those fossils people had to choose between. Much of the content was recycled from generation I.