That’s basically just a bus up the coast of Uruguay and a bit of Rio Grande do Sul? I did the same route in the opposite direction, via Tacuarembo, mostly on horseback. Extremely uncomfortable, but an interesting week nonetheless.
You might be envisioning a more direct route that doesn't include the Foz do Iguaçu part (maybe crossing the border in Uruguaiana or something). I bet that exists as a commercial bus route option too, but the Foz do Iguaçu stopover is all the way up at the triple border of Argentina, Brazil, and Uruguay. So the Brazilian border-skirting for this trip includes all of Rio Grande do Sul, all of Santa Catarina, and a bit of Parana, then back down again on the Brazilian side after crossing the border.
Edit: Yes, it looks like you could totally do that (Buenos Aires to Uruguaiana, then Uruguaiana to Porto Alegre) and save many hours of travel, or even cut more directly through central Uruguay and save even more time. We took the longer option because we wanted to visit Iguaçu Falls and the Itaipu dam, which were both spectacular.
You might be envisioning a more direct route that doesn't include the Foz do Iguaçu part (maybe crossing the border in Uruguaiana or something). I bet that exists as a commercial bus route option too, but the Foz do Iguaçu stopover is all the way up at the triple border of Argentina, Brazil, and Uruguay. So the Brazilian border-skirting for this trip includes all of Rio Grande do Sul, all of Santa Catarina, and a bit of Parana, then back down again on the Brazilian side after crossing the border.
Edit: Yes, it looks like you could totally do that (Buenos Aires to Uruguaiana, then Uruguaiana to Porto Alegre) and save many hours of travel, or even cut more directly through central Uruguay and save even more time. We took the longer option because we wanted to visit Iguaçu Falls and the Itaipu dam, which were both spectacular.