VAZ, I mostly agree with you. The bolter is a point weapon. The Heavy Bolter may not be, but the individual SM weapon is. The armour piercing explosive bolts don't have that much of an area effect as a liquidizing effect when they explode inside a target. That's the idea behind the Marines, they go kill things that don't die easily. If it was easy to kill they'd send in the IG.
However I disagree with the XM-25 comparison, I'd say more the South African PAW-20 https://www.youtube.com/watch?v=ofYkJpxRX2c http://en.wikipedia.org/wiki/Neopup_PAW-20
I agree that with a sniper round there isn't much need for an explosive payload against humans, however there are explosive rifles around and being used for long range kills. An explosive payload will hit just as hard at 2000m as it does at 200m. Of the 14 listed longest sniper kills on Wiki, 3 of them use .50cal Raufoss rounds which are explosive and one used a 14.5x114mm wich can fire explosive rounds as well.
The bolt is vastly over kill to kill a human, it is designed to kill without any chance of survival. Instead of punching a small permanent wound channel with a slightly larger stretch channel it is designed to explode inside a target and lacerate the vital organs, even if they have not been hit directly by the bullet. Think Traitor Marines with their redundant organs, think Ork with their extreme resistance to injury and think Tyrranid with whatever hellspawn internals they have.
It may not be a long ranged precision weapon like an M24, but it is as much of a point weapon as an M14 is. You can't miss fast enough to win a gunfight.