He had the resources to fight the way he did. Probably only a handful of Generals in history have ever had at their disposal what he did.
He was also fighting an enemy with limited supplies, resources, men and money. That they lasted as long as they did is a testament to the CSA.
Time was on his side, so was the money, the manpower, and as I mentioned - the resources. Plus he had a President who backed him 100%.
Tactically, Grant was an amateur. The only reason he won the war was because when others turned around after their first bloody nose, he pushed on. And on. And on. And on.
He lost over 55% of his men in that campaign.
It still took him almost a year to take Richmond even after all that loss.
Any General given those sets of circumstances and combined with his deplorable tactics of continuous frontal assaults without care given to casualties, will eventually win the war.
The operative words being “win the war”. There us no second place prize in war. While his tactical abilities were average at best, his strategic thinking was head and shoulders above his peers. Before the war ended, Grant would accept the surrender of 3 Confederate armies.
Time was on his side...
Actually, time wasn’t on his side. In 1863, right after Gettysburg and Grant’s great victory at Vicksburg, Lincoln had to deal with serious draft riots. By 1864, an election year, there was tremendous pressure for Lincoln to end the war, which is why Lincoln promoted Grant in March. There were great expectations for Grant to end the war quickly, which I believe led to his decision to go up the middle at Cold Harbor.
The failure of the Overland Campaign to end the war led to Lincoln being abandoned by the Republican Party. He had to form his own Union Party.