>>44430844So my theory is that "Evolution" aids a pokemon in terms of battle. When they evolve they become more adept at fighting or using whatever tools they've been gifted with to fight. It takes a lot of practice and their bodies have to adjust but they can manage. Look at Ash's Riolu for example, it fights as hard as it can and its less than a year old.
Mentally Evolution does add something, they still may be lacking in experiences and knowledge, but it increases their capacity to learn new stuff. For example a level 100 Gardevoir or Alakazam who's been alive for 1 week has high mental capabilities and can probably learn new things really quickly, they are just very naive to stuff because they just don't have the life experience. Combat wise though, they are amazing and fight like seasoned Pokemon. The anime however does a very good job at showing level and powerful moves don't mean shit unless you got good technique and strategies to go with them, so a good trainer or mentor helps a lot.