I can't imagine what caused the blowup of that Barnes, but off the cuff, I'd say the velocity was high and the impact was too much for the bullet - but that's pure conjecture on my part. No telling what may have been wrong with that particular bullet, or what it may have impacted 3' from the animal (heavy grass or twig or something) which might have started expansion and thus caused the initial impact on game to be catastrophic failure. Hard to guess on a situation like this.
I've shot a number of white-tails with monoliths, ranging from small-ish (120lbs) on up to pretty good sized (160-175lb) and the results have pretty well been the same. Now, I use the Nosler E-Tip, because it doesn't foul my bores as badly as the Barnes, but the performance should be similar. My shots have been from bow range (<30yds) on out to about 200yds, with impact velocities ranging from 3350+ down to 2800fps. With all but one shot, the entry has been caliber-sized, and the exit has been half-dollar sized or maybe just bigger. Tracking has been easy on all but one - and that one was my fault for hitting a little back and busting the liver and left lung. Blood trail didn't start for about 75yds or so, but only lasted maybe 50-60yds, and Ray Charles could have followed it once it started. I had one shot not exit the animal, and that one went corner to corner on a big doe at 200yds. It was a 180gr from my 300Wby, and the deer was standing just so for the shot, the bullet entered the left shoulder, at the front, through the joint, through the chest cavity, back along the right side, through the rear hip joint, and stopped right under the hide on the back edge of her ham. She was just over 100lbs dressed, which put her at about 140-155lbs estimated live weight. Jawbone said she was 5.5yrs old, according to my notes. Linear penetration was over 4', closer to 5'.
I wouldn't trade the performance of E-Tips from my Weatherbys for any other bullet at this point, based on my field experience. I can't speak directly to the Barnes because I haven't taken game with them. They're not as hard as the gilding metal alloy of the E-Tip and Hornady GMX, so they won't hold together as well under extreme duress, but that's like saying they're only atom bomb proof, not hydrogen bomb proof...
If I were shooting a 6.5 at thin skinned game, and expected ranges to vary from potentially close to very far, I'd strongly consider the E-Tip as a handloading proposition. I shoot the 130gr in my 270Wby (mv 3420fps at best accuracy) and I shoot the 180gr in my 300Wby (mv 3280fps). In the 6.5, you're limited to 120gr weight, though, so maybe that's not ideal. Regardless, there are good options out there. Good luck!