Except OEM's don't make radiators. My replacement Koyo rad was much better than the Calsonic / Nissan OEM spec one. Had two distinct cores vs one larger one with a crimp in it - ie no cirulation between cores.
Denso makes for a lot of OEM's, so your back to specs.
There certainly are bad and good in the aftermarket, but with radiators I don't think OEM are always best.