Its a fine coolant so long as your system is sealed. Problems happen when oxygen gets involved.
If I just filled an engine, I wouldnt flush it out. Just run it and swap out in 5 years.
Dexcool gets blamed for intake gasjets all teh time, some if it justified, but in teh case of teh 1996-2002 Vortec 305/350 is teh hrrible intake gasket design and the way the intake bolts dont apply their forces perpendicular to teh gasket face, they put the head, teh gasket, and the intake manifold in a state of shear. PLUS the stock heads are iron and the intake is aluminum, everytime that engine ehats up and cools down, teh dissimilar expansion rates, in a state of shear, cause the gaskets to roll and break apart. Another case where GM has swapped out durability for ease/speed of install on teh assembly line.