You hit the Giant Chasm much earlier in BW2 so the Pokemon there are not as high level. Over by P2 Laboratory there are some around 55-58. Any better places for basic level up training?
On Victory Road, you can fight level 40-70 Poliwraths when going through bubbling spots while surfing. Another place would be at the entrance of Dragonspiral Tower during Winter in the Double grass you can fight level 63-66 Pokemon
In the Nature Preserve, you can catch a Lv.100 Magikarp (By fishing) or Gyarados (In rippling water).