I think you're applying modern thought to "old" style of fighting. If what you say is correct, the armies would never have "lined up" for battle. They never would have attacked head on, which both the Union and Confederate did. And they definitely never would have marched in battle formation up hill to attack the high ground. And they never would have attacked entrenched enemy over half a mile of open ground with a bayou in front of the entrenchments (as my ancestor's unit did at the Battle of Big Black River MS in 1863).
I'm not saying Grant was morally right in his tactics, simply that they did work. Battle tactics had not caught up with the weaponry that developed during that time period. And, yes, I know that the flanked, etc. But the main thrusts were still line up across from each other and charge.