I don't think they're as bad as some think. If they make wise decisions this off-season, they can be competitive next year. It's less about Goff making them 5 games better and more about a new coaching staff making them better. They were the #32 ranked defense in 2020. If Aaron Glenn is the rising star the league thinks he is and the Lions make some smart additions, they could find themselves having a decent defense in 2021 (especially with Aubrey Pleasant developing the talent they have in the secondary).
In that scenario, Goff doesn't need to be Tom Brady. Anthony Lynn is one of the best in the NFL at scheming up running games imo. The Lions have a solid OL on paper. And D'Andre Swift showed well as a rookie (averaging 4.6 yards per carry and looking like a legitimate passing game weapon). If Goff can get back to playing efficient, smart football, that team is capable of being a thorn in the side of the NFCN. How many people thought McVay could win 11 games with the team Fisher left him? I'm not saying Matt Campbell is McVay, but I am saying that the Lions aren't the 2009 Rams. They have talent.