The union struggled with desertions.
Actually both sides struggled with desertions.
The glue that stemmed the desertion tide for the Union was the slavery issue. Their troops weren't willing to die to preserve tariffs. Many would be willing to die to abolish slavery. So as the war stretched into an effort of several years abolition became the force that made it possible for the Union to continue to field a competitive army at all.
So to argue that the North could have won without abolition as an issue is unequivocally to insist that the North didn't need an army. There is not and never has been a credible refutation of that.
I therefore assert that this article is cut from the same cloth as analysis of the American Revolution which fail to note the contemporaneous political and military situation in Europe as a factor.
Disclaimer: my ancestors didn't immigrate to North America until the 1880s. I have no dog in the fight.
No doubt a component of the Union army was fanatical abolitionists, but a not insignificant component of the Union was drafted.
Apart from that, what were the abolitionists fighting for that first two years when abolishing slavery wasn't on the table? Did they not even believe their own Commander in Chief either? They thought he was lying too?
The truth of what you are saying is found in the popular songs of the time.
The Battle Hymn of the Republic is a great example of the Union picking a song which would motivate the troops with a moral crusade instead of one against tarriffs.
The cynical purpose of the Union leadership was to use slavery as a wedge issue even though it was a secondary issue the origins of the conflict. U.S. Grant cared not whether slaves were found freed or not, as he kept his slaves even after the war.
That's the way the Democrats and their 'moderate' Republicrats would see it.