For whatever its worth.
There is a local rebuilder of 6.5's that insert every block they use (inner bolts)
They tell me that they have not had any failures since using the inserts.
IMHO the fellow you spoke with is misinformed and needs to get up to speed.
Now if $$$$$ are not an issue, by all means get a brand new AMG/GEP P400 engine.
Now for the rest of us Poor souls I will take an inserted block any day.
I hate drilling materials out of the block too, but the truth of the matter is that the insert strengthens the area and actually pulls things together as well as removes the spreading stresses from the area of the outer bolt holes.
Splayed main caps would be a super deal if you could start with a block that did not have any outer holes already drilled.
The problem is the wedging action of the threads in the outer bolt holes.
Once you eliminate that problem and actually reverse the process, breakage is no longer an issue.
MGW