It's arguable that SHA-3 is better understood than SHA-2, at least in the open research community. The rationales behind every component of SHA-3 are well documented, and the design is very conservative, both in structure and number of rounds. More so than SHA-2.
It is in theory possible that a new technique could break SHA-3 and not SHA-2, but the opposite seems far more plausible.
As far as I can tell, the increase from 18 to 24 rounds was not NIST's call, but due to the zero-sum distinguishers found on Keccak-f, which made it no longer "hermetic": http://keccak.noekeon.org/NoteZeroSum.pdf
How is "none" more than "none"?