Grant was able to establish himself permanently in the vicinity and did not withdraw -- which it had been Johnston's objective to force him to do, if he couldn't wreck Grant's force -- whereas the Confederates, driven from the field on the second day by Grant's reinforcements, retreated to Mississippi.
I've thought about Shiloh a long time, and the Confederates basically didn't have the resources to do what the lay of the field required. Grant's dispositions defended his key landing in sufficient depth to prevent the Southerners from doing what they needed to do in one day's fighting.
JMHO, if Johnston's troops somehow could have approached Grant's base area under cover and avoided Prentiss, they might have had a chance of carrying the field. But fighting through Prentiss and the Hornet's Nest/Peach Orchard line was just too much. They spent themselves before they got close to endangering Grant's lodgement at the landing.
The battle was a mismatch, with Southern forces overmatched by the job to be done and outnumbered by Union forces in the operating area. It was a significant Union victory.
LG:
I can concede, but I always thought that Johnston’s death was the damper on the Confederate drive towards the river, etc. :)