I found an amazing female Trace Ralts and I was so excited... until I found out it had a lonely nature. Ouch. Gallade would be fine with it, but it’s female... so, do you think a Lonely nature Gardevoir can be done in game?
Honestly, Natures don't matter that much in-game as everything can be overcome by over levelling. So, Lonely isn't the best nature, but it isn't enough to go search for another Ralts unless you absolutely want a Timid or Modest one as it is for in-game purposes. Source: Experience.