Cooper absolutely wins, maybe by more than 5 points. He'd probably have won in 2020 too if he had run for the Senate rather than for reelection (he'd be put to better use in the Senate - after all, he doesn't have all that much power as Governor given that the GOP controls the Legislature and that same Legislature has stripped away some of his powers).
Cooper being in the Governor's seat matters a lot, actually. Republicans currently don't have a supermajority which means they can't override his veto, which has forced them to work with Democrats more on some issues (like medical marijuana and medicaid expansion, both of which seem to have a realistic chance of passing). And of course the most important thing is that Cooper's presence plus the loss of the supermajority prevents Republicans from passing a bunch of extremist crap like they have been in other states.
Fair enough and I’m aware of that, but the NCGOP still has stripped away some of the governor’s powers (such as giving him the power of signing off on redistricting). And I maintain that an extra vote in the Senate (though there’s no telling how NC going blue might impact the GA runoffs) matters a lot more than the NC governorship. NC governorship impacts only North Carolinians; a Senate seat impacts all Americans.
The stripping away of veto power for redistricting dates to Democrats in the 90s.
I think you can make a pretty persuasive argument that having Roy Cooper as governor of North Carolina has a bigger impact on the American people than having one more Democratic vote in the Senate. Now if it was two more Democratic votes, that's a different story, but Roy Cooper going to Washington and abandoning NC to, idk, Mark Robinson? probably gives us a timeline where the American people are slightly worse off due to the heinous impact Republican control has in North Carolina.