I'm sure there are .22lr uppers that can achieve match grade accuracy out of the box, just like I am sure there were yugos (the car) back in the day that would make it to 100K miles without needing a single repair. However as a general rule it doesn't happen. If I remember right Nordic made some higher end barrels/uppers and they were probably priced accordingly. Eley ammo isn't exactly bulk ammo either.
I think the OP's expectation that a mass produced CMMG .22lr conversion upper will outperform his Marlin is a bit optimistic unless he's willing to invest more time and money than it's worth. Can you get one from the factory that is very accurate? Sure. One can always win the lottery when it comes to manufacturing variances, just don't count on it.