The ford OEM egr cooler are crap, unless he replaced them by specialty diesel parts, like sinister or something, aswell as ran preventative, shouldnt have happened. The big thing to prevent the 6.0 turbo failure was to run a cetane booster in the fuel to reduce soot production. Also subpar functioning EGR coolers would cause soot build up that would also clock vains in the turbo.
The big differences between the 7.3 and 6.0 and the 6.4 and 6.7, is emissions. Though the 6.0 had some emissions, the truck didnt have monitoring systems on anything but EGR, and were removable. A correctley built/maintained 6.0 can easily go 3-500k miles. But the 6.4-6.7, when removing the emissions has to be tuned correctley, but being on the PSD forums for 2 years, most people would run race tunes or heavy duty tunes, and grenade that engine. The internals like the crank and cams cant support all the power you through out at it. Another things that happens with 6.4 that is very common and catastrophic, those turbos are more prone to seal failure than 6.0, and would cause oil to be pumped into the dpf and clog it, then the dpf tell the engine to go into regen, which cause cylinder 7-8 to get burnt, and cause total engine failure. The 6.7 is probably the worse of the PSD. Thier turbos are made inhouse be ford if im not mistaken, and use ceramic balberians and they are 90k mile turbos, and it causes the same issues as 6.4 with the regen. Also that engine rejects tunes like people reject the inlaws.
Im not saying the PSD is a good engine, they all suck except the 7.3. But from my experience and being on the other forum, i have seen a lot of stuff. I liked my 6.0 but i hated how expensive it was and i prolly wouldnt get one again. 6.4 and 6.7 are a million times stronger than the 6.0 but 6.0 can be built up well and tuned nicely, where the newer engines have more moving parts that fail and fail big, and reject tunes(as in relability, known to blown an engine with race or tow tune within 20-30k). At my old work, used to be right next to Left Coast Diesel in livermore, where i was, and they say more failures in 6.4's, and more maintenance and preventative stuff in 6.0.
When the 6.4 is running good, its a monster.
Im not in anyway saying your wrong, its just what i have seen, and we all have our own prejudices toward certain things and we wont be persuaded by a forum post.