I feel like something odd is going on. Are you exploring much and capturing wild pokemon? I haven’t played the latest gen but Let’s Go, Shield, and Legends Arceus were all very difficult to not get over leveled in most of the time. I tend to spend a lot of time running around and trying to get at least one of every species that I come across. The team wide experience can really get you over leveled fast unless you are rotating mons on your team frequently.
As far as I know, the Xbox One and PS4 started the trend of reading nothing from the disc after install. The disc just acts as instalation media and a physical authenticator.