hmmm this is a very nice topic to discuss. I think that since its origins, one of the most important features of pokemon was trading and it still is imo. On the other hand tho, I understand how frustrating it is to evolve a pokemon by trading, especially feebas to milotic or porygon. And it's even more frustrating when u have to pay for the Internet connection for trading, so yeah, this is a point tbh. But it would also be really sad just changing these pokemon's evolution to just levelling up. So, imo they should stay the way they are. I think it's a nice feature, but i do agree on the fact that it's frustrating, especially if u take into account the fact that u basically have to pay to evolve ur pokémon.