While I do agree, it's maybe not so cut and dry. Playing a lot of minutes in all situations, even on easy mode, could improve his endurance. He also may not get as good an up close experience due to COVID protocols. For instance, they don't do full film study sessions I don't think.
That said, I do agree it's better to keep him up at the pro level. If nothing else it guards against the possibility he's unavailable to them perhaps for the rest of the season depending on how the OHL proceeds on a playoff structure and the Memorial Cup. It sounds like they're at least six weeks away from a restart with no firm plan established yet so he'll probably have at least another couple weeks before it's a factor.