Roth didn’t emerge in the last 50 years (otherwise I’d agree with you).* I’ve enjoyed books by all six but I agree with King on this one. The Goldfinch was, page for page, probably the best reading experience I’ve ever had. I adore that book. Franzen is less lovable but undeniably talented and, for me at least, more fun to read than the people who influenced him (Pynchon, DeLillo, etc)

*edit: I didn’t read the quote carefully. Looks like he really is saying those two are the best American novelists, full stop. Bold and kind of interesting statement on King’s part.