I gotta admit... this pretty much killed the hype I had for this game.
Level grinding is going to be a massive pain. Unless Game Freak brings back the Vs. Seeker in some form so we could rematch trainers, then it's more than likely that some of our party members are gong to be lower leveled than we'd like, especially catcing new ones.
The big problem here is that, to put it bluntly, it's a huge waste of Pokeballs. Pokeballs cost money, which means you have to fight more Trainers. Again, not a problem without some sort of player rematch system. But if not? Then people are screwed, because how can you level up your Pokemon if you don't have Pokeballs or money or spend? Another issue is that you're not even guaranteed a catch, which means you have to use more Pokeballs, and then you have to replenish that stock.
Great Balls and Ultra Balls are going to become more of a rarity than they are currently which is going to be interesting.