The current game mechanics do not limit you in any such way notable. Its a grind, and the grind is the same for every pokemon. Some require more dedication, or hours. But they all end up at the same place. If you want to use a normally not used pokemon, go head! But it may take longer than say a over used pokemon. Be ready for a struggle if it isen't mainstream, being normal is easy. But being unique takes a bit, but you'll all end up at the same place.