well yes and no. IMO. there ARE known engineered deficiencies in the 6.0L diesel. Thats not disputed. The will fail if left stock, or even faster if left stock and hotrodded. theres a large aftermarket support for them now. that will correct every deficiency. stud the heads, delete the egr, relocate the engine oil cooler, and they will work really good after. this heui system is very fickle to engine oil too. correct weight and always clean and fresh. Theres a guy here in fort Mac that put down 1150 HP to the wheels in his 6.0L race truck as of last season.
So no, they're not bad if you know what your doing with them. But I'm still building a big bad cummins for my own. I like the truck part, of ford trucks, over the other manufactures. As far as chassis, and interior are concerned. even transmissions. the 4r100 and 5r110 are STOUT autos in stock form. the ZF6 for the stick option. Stout gearbox. they do really good that way. just really dropped the ball in the engine compartment IMO.