If Game Freak is to release two games at the same time without much differences, then it makes sense for them to include version exclusives. Trading Pokémon is an important aspect of Pokémon, which Game Freak strongly encourages players to do, as players are likely to trade for Pokémon that aren't in their games. With that, I don't consider version exclusives to be outdated at all. The thing about Pokémon Legends: Arceus is that it is meant to be a side game to get players involved in the story and doesn't really encourage trading. You also said that trading makes completing the Pokédex more complicated. I disagree. I think it makes it easier because, by trading, you don't have to put in much work to obtain certain Pokémon, especially when many people in the community are willing to help out players out of kindness. The Union Circle feature is different because it is easier to get on a site like this and/or Discord and find someone to trade with rather than find someone that you trust to let you connect to their game and catch their version exclusives. However, this does raise the question: does Game Freak need to release two games per generation? Maybe not. Pokémon can definitely thrive with a single game release, but if every Pokémon was found on a single game, it could discourage trading. Like, for example, when I completed Pokémon Legends: Arceus, I didn't make a single trade to complete the Pokédex.