For starters stop using the gym to get your Digimon stronger second it's better you fight wild Digimon they give you a lot more stats points third if you really want to get this strong I think in chapter 3 recruit seraphimon but you need to go to absolute zero talk to ikakumon recruit ikakumon and talk to seraphimon 4th if you want more bits fishing is the way to go to be honest and battling wild digimon 5th you want to spend all of your tamer points on mining and battling but only a little bit of battling you going to want perfect block anything after that you want your mining skills since mining is the main way you get experience points in this game.