Digimon world next order: did I screw up?

I've been playing for a few hours and my original Digimon both reached ultimate level with stats in the 2000s before dying

They died a couple of days apart, so my replacement partner reached about 600 stats and evolved to rookie before my other ultimate died.

So now I have one rookie and one idk newborn. Problem is that my rookie is kinda useless. It doesn't really seem to do as much damage as it should. I looked up grind spots online, and I'm getting destroyed against enemies that I should be able to easily farm. My rookie just kind of stands there doing nothing unless I command him to attack, and his attacks are weak as shit.

And when I do manage to win, both of my Digimon are getting only +1 to stats. At this rate both of my Digimon are going to die of old age before they're able to do anything.

What should I be doing in this situation? Can this imbalance be saved, or should I just run around in circles until both partners die and I can start again fresh?