The first thing to consider is going to be how each looks in terms of their fWAR/bWAR/WARP splits. Here’s how each has performed the past four seasons:
Donaldson was dealing with shoulder and calf injuries in 2018 when the Blue Jays traded him to the Indians, so those WAR numbers from that season need to be taken with a grain of salt. He also faced some injury issues in 2017 with the same calf issue that ailed him in 2018, so his numbers are a little lower than they could have been due to that as well as he only played in 113 games that season.
Another way we can look at it is seeing how much WAR Donaldson would have accumulated if he had gotten the same amount of Plate Appearances as Nolan has had in the past four seasons.
Nolan had 2,711 PAs from 2016-2019 while Donaldson had 2,074. If we look strictly at fWAR, Nolan accumulated 22.4 fWAR in those four seasons while Donaldson accumulated 18.9.
If we assume he would’ve gotten the same amount of PAs as Nolan, his total fWAR would’ve been 24.7, meaning he was slightly more efficient than Nolan the past four seasons.
At the very least, he’s produced pretty similarly to Nolan the past four seasons when he’s been available. I don’t expect that he’d outpace Nolan going forward due to his age, but he would still likely produce at a level that would still make him an upper echelon third baseman (probably within the 4-5 WAR range, which would be more than acceptable on this roster).